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Factorials Examples Taylor Series Expansions Extensions Generalized Factorials and Taylor Expansions Michael R. Pilla Winona State University April 16, 2010 Michael R. Pilla Generalizations of the Factorial Function

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Page 1: Generalized Factorials and Taylor Expansionscourse1.winona.edu/eerrthum/UndergradResearch/... · Generalized Factorials and Taylor Expansions Michael R. Pilla Winona State University

Factorials Examples Taylor Series Expansions Extensions

Generalized Factorials and Taylor Expansions

Michael R. PillaWinona State University

April 16, 2010

Michael R. Pilla Generalizations of the Factorial Function

Page 2: Generalized Factorials and Taylor Expansionscourse1.winona.edu/eerrthum/UndergradResearch/... · Generalized Factorials and Taylor Expansions Michael R. Pilla Winona State University

Factorials Examples Taylor Series Expansions Extensions

Factorials

Recall the definition of a factorial

n! = n·(n−1)···2·1 =

(n−0)(n−1)(n−2)···(n−(n−2))(n−(n−1)).

For S = {a0, a1, a2, a3, ...} ⊆ N,

Define n!S = (an − a0)(an − a1) · · · (an − an−1).

Pros:

We have a nice formula.

It works on subsets of N.

Cons:

It is not theoreticallyuseful.

What about the order ofthe subset?

Michael R. Pilla Generalizations of the Factorial Function

Page 3: Generalized Factorials and Taylor Expansionscourse1.winona.edu/eerrthum/UndergradResearch/... · Generalized Factorials and Taylor Expansions Michael R. Pilla Winona State University

Factorials Examples Taylor Series Expansions Extensions

Factorials

Recall the definition of a factorial

n! = n·(n−1)···2·1 = (n−0)(n−1)(n−2)···(n−(n−2))(n−(n−1)).

For S = {a0, a1, a2, a3, ...} ⊆ N,

Define n!S = (an − a0)(an − a1) · · · (an − an−1).

Pros:

We have a nice formula.

It works on subsets of N.

Cons:

It is not theoreticallyuseful.

What about the order ofthe subset?

Michael R. Pilla Generalizations of the Factorial Function

Page 4: Generalized Factorials and Taylor Expansionscourse1.winona.edu/eerrthum/UndergradResearch/... · Generalized Factorials and Taylor Expansions Michael R. Pilla Winona State University

Factorials Examples Taylor Series Expansions Extensions

Factorials

Recall the definition of a factorial

n! = n·(n−1)···2·1 = (n−0)(n−1)(n−2)···(n−(n−2))(n−(n−1)).

For S = {a0, a1, a2, a3, ...} ⊆ N,

Define n!S = (an − a0)(an − a1) · · · (an − an−1).

Pros:

We have a nice formula.

It works on subsets of N.

Cons:

It is not theoreticallyuseful.

What about the order ofthe subset?

Michael R. Pilla Generalizations of the Factorial Function

Page 5: Generalized Factorials and Taylor Expansionscourse1.winona.edu/eerrthum/UndergradResearch/... · Generalized Factorials and Taylor Expansions Michael R. Pilla Winona State University

Factorials Examples Taylor Series Expansions Extensions

Factorials

Recall the definition of a factorial

n! = n·(n−1)···2·1 = (n−0)(n−1)(n−2)···(n−(n−2))(n−(n−1)).

For S = {a0, a1, a2, a3, ...} ⊆ N,

Define n!S = (an − a0)(an − a1) · · · (an − an−1).

Pros:

We have a nice formula.

It works on subsets of N.

Cons:

It is not theoreticallyuseful.

What about the order ofthe subset?

Michael R. Pilla Generalizations of the Factorial Function

Page 6: Generalized Factorials and Taylor Expansionscourse1.winona.edu/eerrthum/UndergradResearch/... · Generalized Factorials and Taylor Expansions Michael R. Pilla Winona State University

Factorials Examples Taylor Series Expansions Extensions

Factorials

Recall the definition of a factorial

n! = n·(n−1)···2·1 = (n−0)(n−1)(n−2)···(n−(n−2))(n−(n−1)).

For S = {a0, a1, a2, a3, ...} ⊆ N,

Define n!S = (an − a0)(an − a1) · · · (an − an−1).

Pros:

We have a nice formula.

It works on subsets of N.

Cons:

It is not theoreticallyuseful.

What about the order ofthe subset?

Michael R. Pilla Generalizations of the Factorial Function

Page 7: Generalized Factorials and Taylor Expansionscourse1.winona.edu/eerrthum/UndergradResearch/... · Generalized Factorials and Taylor Expansions Michael R. Pilla Winona State University

Factorials Examples Taylor Series Expansions Extensions

Factorials

Recall the definition of a factorial

n! = n·(n−1)···2·1 = (n−0)(n−1)(n−2)···(n−(n−2))(n−(n−1)).

For S = {a0, a1, a2, a3, ...} ⊆ N,

Define n!S = (an − a0)(an − a1) · · · (an − an−1).

Pros:

We have a nice formula.

It works on subsets of N.

Cons:

It is not theoreticallyuseful.

What about the order ofthe subset?

Michael R. Pilla Generalizations of the Factorial Function

Page 8: Generalized Factorials and Taylor Expansionscourse1.winona.edu/eerrthum/UndergradResearch/... · Generalized Factorials and Taylor Expansions Michael R. Pilla Winona State University

Factorials Examples Taylor Series Expansions Extensions

Factorials

Recall the definition of a factorial

n! = n·(n−1)···2·1 = (n−0)(n−1)(n−2)···(n−(n−2))(n−(n−1)).

For S = {a0, a1, a2, a3, ...} ⊆ N,

Define n!S = (an − a0)(an − a1) · · · (an − an−1).

Pros:

We have a nice formula.

It works on subsets of N.

Cons:

It is not theoreticallyuseful.

What about the order ofthe subset?

Michael R. Pilla Generalizations of the Factorial Function

Page 9: Generalized Factorials and Taylor Expansionscourse1.winona.edu/eerrthum/UndergradResearch/... · Generalized Factorials and Taylor Expansions Michael R. Pilla Winona State University

Factorials Examples Taylor Series Expansions Extensions

Factorials

Recall the definition of a factorial

n! = n·(n−1)···2·1 = (n−0)(n−1)(n−2)···(n−(n−2))(n−(n−1)).

For S = {a0, a1, a2, a3, ...} ⊆ N,

Define n!S = (an − a0)(an − a1) · · · (an − an−1).

Pros:

We have a nice formula.

It works on subsets of N.

Cons:

It is not theoreticallyuseful.

What about the order ofthe subset?

Michael R. Pilla Generalizations of the Factorial Function

Page 10: Generalized Factorials and Taylor Expansionscourse1.winona.edu/eerrthum/UndergradResearch/... · Generalized Factorials and Taylor Expansions Michael R. Pilla Winona State University

Factorials Examples Taylor Series Expansions Extensions

Factorials

Recall the definition of a factorial

n! = n·(n−1)···2·1 = (n−0)(n−1)(n−2)···(n−(n−2))(n−(n−1)).

For S = {a0, a1, a2, a3, ...} ⊆ N,

Define n!S = (an − a0)(an − a1) · · · (an − an−1).

Pros:

We have a nice formula.

It works on subsets of N.

Cons:

It is not theoreticallyuseful.

What about the order ofthe subset?

Michael R. Pilla Generalizations of the Factorial Function

Page 11: Generalized Factorials and Taylor Expansionscourse1.winona.edu/eerrthum/UndergradResearch/... · Generalized Factorials and Taylor Expansions Michael R. Pilla Winona State University

Factorials Examples Taylor Series Expansions Extensions

Generalized Factorials

Bhargava: Let’s look at prime factorizations and play a gamecalled p-ordering for each prime p.

If the ordering works for all primes simultaneosly, then we canachieve nice formulas.

Theorem

If S = {ai} is p-ordered for all primes simultaneously then

n!S = |(an − a0)(an − a1) · · · (an − an−1)|.

If a subset cannot be simultaneously ordered, the formulas areugly (if and when they exist) and the factorials difficult tocalculate.

Goal: Extend factorials to “nice”, “natural” subsets of N thathave closed formulas.

Michael R. Pilla Generalizations of the Factorial Function

Page 12: Generalized Factorials and Taylor Expansionscourse1.winona.edu/eerrthum/UndergradResearch/... · Generalized Factorials and Taylor Expansions Michael R. Pilla Winona State University

Factorials Examples Taylor Series Expansions Extensions

Generalized Factorials

Bhargava: Let’s look at prime factorizations and play a gamecalled p-ordering for each prime p.

If the ordering works for all primes simultaneosly, then we canachieve nice formulas.

Theorem

If S = {ai} is p-ordered for all primes simultaneously then

n!S = |(an − a0)(an − a1) · · · (an − an−1)|.

If a subset cannot be simultaneously ordered, the formulas areugly (if and when they exist) and the factorials difficult tocalculate.

Goal: Extend factorials to “nice”, “natural” subsets of N thathave closed formulas.

Michael R. Pilla Generalizations of the Factorial Function

Page 13: Generalized Factorials and Taylor Expansionscourse1.winona.edu/eerrthum/UndergradResearch/... · Generalized Factorials and Taylor Expansions Michael R. Pilla Winona State University

Factorials Examples Taylor Series Expansions Extensions

Generalized Factorials

Bhargava: Let’s look at prime factorizations and play a gamecalled p-ordering for each prime p.

If the ordering works for all primes simultaneosly, then we canachieve nice formulas.

Theorem

If S = {ai} is p-ordered for all primes simultaneously then

n!S = |(an − a0)(an − a1) · · · (an − an−1)|.

If a subset cannot be simultaneously ordered, the formulas areugly (if and when they exist) and the factorials difficult tocalculate.

Goal: Extend factorials to “nice”, “natural” subsets of N thathave closed formulas.

Michael R. Pilla Generalizations of the Factorial Function

Page 14: Generalized Factorials and Taylor Expansionscourse1.winona.edu/eerrthum/UndergradResearch/... · Generalized Factorials and Taylor Expansions Michael R. Pilla Winona State University

Factorials Examples Taylor Series Expansions Extensions

Generalized Factorials

Bhargava: Let’s look at prime factorizations and play a gamecalled p-ordering for each prime p.

If the ordering works for all primes simultaneosly, then we canachieve nice formulas.

Theorem

If S = {ai} is p-ordered for all primes simultaneously then

n!S = |(an − a0)(an − a1) · · · (an − an−1)|.

If a subset cannot be simultaneously ordered, the formulas areugly (if and when they exist) and the factorials difficult tocalculate.

Goal: Extend factorials to “nice”, “natural” subsets of N thathave closed formulas.

Michael R. Pilla Generalizations of the Factorial Function

Page 15: Generalized Factorials and Taylor Expansionscourse1.winona.edu/eerrthum/UndergradResearch/... · Generalized Factorials and Taylor Expansions Michael R. Pilla Winona State University

Factorials Examples Taylor Series Expansions Extensions

Generalized Factorials

Bhargava: Let’s look at prime factorizations and play a gamecalled p-ordering for each prime p.

If the ordering works for all primes simultaneosly, then we canachieve nice formulas.

Theorem

If S = {ai} is p-ordered for all primes simultaneously then

n!S = |(an − a0)(an − a1) · · · (an − an−1)|.

If a subset cannot be simultaneously ordered, the formulas areugly (if and when they exist) and the factorials difficult tocalculate.

Goal: Extend factorials to “nice”, “natural” subsets of N thathave closed formulas.

Michael R. Pilla Generalizations of the Factorial Function

Page 16: Generalized Factorials and Taylor Expansionscourse1.winona.edu/eerrthum/UndergradResearch/... · Generalized Factorials and Taylor Expansions Michael R. Pilla Winona State University

Factorials Examples Taylor Series Expansions Extensions

Arithmetic Sets

Example

Consider the arithmetic set A = {2, 9, 16, 23, ...} (i.e. allintegers 2 mod 7). This is p-ordered for all primessimultaneously. Thus

1!A = (9− 2) = 7

= 711!

2!A = (16− 2)(16− 9) = 98

= 722!

3!A = (23− 2)(23− 9)(23− 16) = 2058

= 733!

n!A = 7nn!

Example

Let S = aN + b of all integers b mod a. The natural ordering isp-ordered for all primes simultaneously. Thus

n!aN+b = ann!

Michael R. Pilla Generalizations of the Factorial Function

Page 17: Generalized Factorials and Taylor Expansionscourse1.winona.edu/eerrthum/UndergradResearch/... · Generalized Factorials and Taylor Expansions Michael R. Pilla Winona State University

Factorials Examples Taylor Series Expansions Extensions

Arithmetic Sets

Example

Consider the arithmetic set A = {2, 9, 16, 23, ...} (i.e. allintegers 2 mod 7). This is p-ordered for all primessimultaneously. Thus

1!A = (9− 2) = 7

= 711!

2!A = (16− 2)(16− 9) = 98

= 722!

3!A = (23− 2)(23− 9)(23− 16) = 2058

= 733!

n!A = 7nn!

Example

Let S = aN + b of all integers b mod a. The natural ordering isp-ordered for all primes simultaneously. Thus

n!aN+b = ann!

Michael R. Pilla Generalizations of the Factorial Function

Page 18: Generalized Factorials and Taylor Expansionscourse1.winona.edu/eerrthum/UndergradResearch/... · Generalized Factorials and Taylor Expansions Michael R. Pilla Winona State University

Factorials Examples Taylor Series Expansions Extensions

Arithmetic Sets

Example

Consider the arithmetic set A = {2, 9, 16, 23, ...} (i.e. allintegers 2 mod 7). This is p-ordered for all primessimultaneously. Thus

1!A = (9− 2) = 7

= 711!

2!A = (16− 2)(16− 9) = 98

= 722!

3!A = (23− 2)(23− 9)(23− 16) = 2058

= 733!

n!A = 7nn!

Example

Let S = aN + b of all integers b mod a. The natural ordering isp-ordered for all primes simultaneously. Thus

n!aN+b = ann!

Michael R. Pilla Generalizations of the Factorial Function

Page 19: Generalized Factorials and Taylor Expansionscourse1.winona.edu/eerrthum/UndergradResearch/... · Generalized Factorials and Taylor Expansions Michael R. Pilla Winona State University

Factorials Examples Taylor Series Expansions Extensions

Arithmetic Sets

Example

Consider the arithmetic set A = {2, 9, 16, 23, ...} (i.e. allintegers 2 mod 7). This is p-ordered for all primessimultaneously. Thus

1!A = (9− 2) = 7

= 711!

2!A = (16− 2)(16− 9) = 98

= 722!

3!A = (23− 2)(23− 9)(23− 16) = 2058

= 733!

n!A = 7nn!

Example

Let S = aN + b of all integers b mod a. The natural ordering isp-ordered for all primes simultaneously. Thus

n!aN+b = ann!

Michael R. Pilla Generalizations of the Factorial Function

Page 20: Generalized Factorials and Taylor Expansionscourse1.winona.edu/eerrthum/UndergradResearch/... · Generalized Factorials and Taylor Expansions Michael R. Pilla Winona State University

Factorials Examples Taylor Series Expansions Extensions

Arithmetic Sets

Example

Consider the arithmetic set A = {2, 9, 16, 23, ...} (i.e. allintegers 2 mod 7). This is p-ordered for all primessimultaneously. Thus

1!A = (9− 2) = 7 = 711!

2!A = (16− 2)(16− 9) = 98 = 722!

3!A = (23− 2)(23− 9)(23− 16) = 2058 = 733!

n!A = 7nn!

Example

Let S = aN + b of all integers b mod a. The natural ordering isp-ordered for all primes simultaneously. Thus

n!aN+b = ann!

Michael R. Pilla Generalizations of the Factorial Function

Page 21: Generalized Factorials and Taylor Expansionscourse1.winona.edu/eerrthum/UndergradResearch/... · Generalized Factorials and Taylor Expansions Michael R. Pilla Winona State University

Factorials Examples Taylor Series Expansions Extensions

Arithmetic Sets

Example

Consider the arithmetic set A = {2, 9, 16, 23, ...} (i.e. allintegers 2 mod 7). This is p-ordered for all primessimultaneously. Thus

1!A = (9− 2) = 7 = 711!

2!A = (16− 2)(16− 9) = 98 = 722!

3!A = (23− 2)(23− 9)(23− 16) = 2058 = 733!

n!A = 7nn!

Example

Let S = aN + b of all integers b mod a. The natural ordering isp-ordered for all primes simultaneously. Thus

n!aN+b = ann!

Michael R. Pilla Generalizations of the Factorial Function

Page 22: Generalized Factorials and Taylor Expansionscourse1.winona.edu/eerrthum/UndergradResearch/... · Generalized Factorials and Taylor Expansions Michael R. Pilla Winona State University

Factorials Examples Taylor Series Expansions Extensions

Set of Squares

Example

The set Z2 = {0, 1, 4, 9, 16, ...} of square numbers admits asimultaneous p-ordering. Thus

1!Z2 = (1− 0) = 1

2!Z2 = (4− 0)(4− 1) = 12

3!Z2 = (9− 0)(9− 1)(9− 4) = 360

4!Z2 = (16− 0)(16− 1)(16− 4)(16− 9) = 20160

n!Z2 = (n2 − 0)(n2 − 1)(n2 − 4) · · · (n2 − (n − 1)2)

= (n − 0)(n + 0)(n − 1)(n + 1)...(n − (n − 1))(n + (n − 1))

=2n

2(2n − 1)(2n − 2) · · · (n)(n − 1) · · · (1)

=(2n)!

2

Michael R. Pilla Generalizations of the Factorial Function

Page 23: Generalized Factorials and Taylor Expansionscourse1.winona.edu/eerrthum/UndergradResearch/... · Generalized Factorials and Taylor Expansions Michael R. Pilla Winona State University

Factorials Examples Taylor Series Expansions Extensions

Set of Squares

Example

The set Z2 = {0, 1, 4, 9, 16, ...} of square numbers admits asimultaneous p-ordering. Thus

1!Z2 = (1− 0) = 1

2!Z2 = (4− 0)(4− 1) = 12

3!Z2 = (9− 0)(9− 1)(9− 4) = 360

4!Z2 = (16− 0)(16− 1)(16− 4)(16− 9) = 20160

n!Z2 = (n2 − 0)(n2 − 1)(n2 − 4) · · · (n2 − (n − 1)2)

= (n − 0)(n + 0)(n − 1)(n + 1)...(n − (n − 1))(n + (n − 1))

=2n

2(2n − 1)(2n − 2) · · · (n)(n − 1) · · · (1)

=(2n)!

2

Michael R. Pilla Generalizations of the Factorial Function

Page 24: Generalized Factorials and Taylor Expansionscourse1.winona.edu/eerrthum/UndergradResearch/... · Generalized Factorials and Taylor Expansions Michael R. Pilla Winona State University

Factorials Examples Taylor Series Expansions Extensions

Set of Squares

Example

The set Z2 = {0, 1, 4, 9, 16, ...} of square numbers admits asimultaneous p-ordering. Thus

1!Z2 = (1− 0) = 1

2!Z2 = (4− 0)(4− 1) = 12

3!Z2 = (9− 0)(9− 1)(9− 4) = 360

4!Z2 = (16− 0)(16− 1)(16− 4)(16− 9) = 20160

n!Z2 = (n2 − 0)(n2 − 1)(n2 − 4) · · · (n2 − (n − 1)2)

= (n − 0)(n + 0)(n − 1)(n + 1)...(n − (n − 1))(n + (n − 1))

=2n

2(2n − 1)(2n − 2) · · · (n)(n − 1) · · · (1)

=(2n)!

2

Michael R. Pilla Generalizations of the Factorial Function

Page 25: Generalized Factorials and Taylor Expansionscourse1.winona.edu/eerrthum/UndergradResearch/... · Generalized Factorials and Taylor Expansions Michael R. Pilla Winona State University

Factorials Examples Taylor Series Expansions Extensions

Set of Squares

Example

The set Z2 = {0, 1, 4, 9, 16, ...} of square numbers admits asimultaneous p-ordering. Thus

1!Z2 = (1− 0) = 1

2!Z2 = (4− 0)(4− 1) = 12

3!Z2 = (9− 0)(9− 1)(9− 4) = 360

4!Z2 = (16− 0)(16− 1)(16− 4)(16− 9) = 20160

n!Z2 = (n2 − 0)(n2 − 1)(n2 − 4) · · · (n2 − (n − 1)2)

= (n − 0)(n + 0)(n − 1)(n + 1)...(n − (n − 1))(n + (n − 1))

=2n

2(2n − 1)(2n − 2) · · · (n)(n − 1) · · · (1)

=(2n)!

2

Michael R. Pilla Generalizations of the Factorial Function

Page 26: Generalized Factorials and Taylor Expansionscourse1.winona.edu/eerrthum/UndergradResearch/... · Generalized Factorials and Taylor Expansions Michael R. Pilla Winona State University

Factorials Examples Taylor Series Expansions Extensions

Set of Squares

Example

The set Z2 = {0, 1, 4, 9, 16, ...} of square numbers admits asimultaneous p-ordering. Thus

1!Z2 = (1− 0) = 1

2!Z2 = (4− 0)(4− 1) = 12

3!Z2 = (9− 0)(9− 1)(9− 4) = 360

4!Z2 = (16− 0)(16− 1)(16− 4)(16− 9) = 20160

n!Z2 = (n2 − 0)(n2 − 1)(n2 − 4) · · · (n2 − (n − 1)2)

= (n − 0)(n + 0)(n − 1)(n + 1)...(n − (n − 1))(n + (n − 1))

=2n

2(2n − 1)(2n − 2) · · · (n)(n − 1) · · · (1)

=(2n)!

2

Michael R. Pilla Generalizations of the Factorial Function

Page 27: Generalized Factorials and Taylor Expansionscourse1.winona.edu/eerrthum/UndergradResearch/... · Generalized Factorials and Taylor Expansions Michael R. Pilla Winona State University

Factorials Examples Taylor Series Expansions Extensions

Set of Squares

Example

The set Z2 = {0, 1, 4, 9, 16, ...} of square numbers admits asimultaneous p-ordering. Thus

1!Z2 = (1− 0) = 1

2!Z2 = (4− 0)(4− 1) = 12

3!Z2 = (9− 0)(9− 1)(9− 4) = 360

4!Z2 = (16− 0)(16− 1)(16− 4)(16− 9) = 20160

n!Z2 = (n2 − 0)(n2 − 1)(n2 − 4) · · · (n2 − (n − 1)2)

= (n − 0)(n + 0)(n − 1)(n + 1)...(n − (n − 1))(n + (n − 1))

=2n

2(2n − 1)(2n − 2) · · · (n)(n − 1) · · · (1)

=(2n)!

2

Michael R. Pilla Generalizations of the Factorial Function

Page 28: Generalized Factorials and Taylor Expansionscourse1.winona.edu/eerrthum/UndergradResearch/... · Generalized Factorials and Taylor Expansions Michael R. Pilla Winona State University

Factorials Examples Taylor Series Expansions Extensions

Set of Squares

Example

The set Z2 = {0, 1, 4, 9, 16, ...} of square numbers admits asimultaneous p-ordering. Thus

1!Z2 = (1− 0) = 1

2!Z2 = (4− 0)(4− 1) = 12

3!Z2 = (9− 0)(9− 1)(9− 4) = 360

4!Z2 = (16− 0)(16− 1)(16− 4)(16− 9) = 20160

n!Z2 = (n2 − 0)(n2 − 1)(n2 − 4) · · · (n2 − (n − 1)2)

= (n − 0)(n + 0)(n − 1)(n + 1)...(n − (n − 1))(n + (n − 1))

=2n

2(2n − 1)(2n − 2) · · · (n)(n − 1) · · · (1)

=(2n)!

2

Michael R. Pilla Generalizations of the Factorial Function

Page 29: Generalized Factorials and Taylor Expansionscourse1.winona.edu/eerrthum/UndergradResearch/... · Generalized Factorials and Taylor Expansions Michael R. Pilla Winona State University

Factorials Examples Taylor Series Expansions Extensions

Twice Triangulars (Squares Modified)

Example

Likewise, one can show the set2T = {n2 + n | n ∈ N} = {0, 2, 6, 12, 20, ...} admits asimultaneous p-ordering. Thus

1!2T = (2− 0) = 2

2!2T = (6− 0)(6− 2) = 24

3!2T = (12− 0)(12− 2)(12− 6) = 720

4!2T = (20− 0)(20− 2)(20− 6)(20− 12) = 40320

n!2T = (2n)!

Michael R. Pilla Generalizations of the Factorial Function

Page 30: Generalized Factorials and Taylor Expansionscourse1.winona.edu/eerrthum/UndergradResearch/... · Generalized Factorials and Taylor Expansions Michael R. Pilla Winona State University

Factorials Examples Taylor Series Expansions Extensions

Twice Triangulars (Squares Modified)

Example

Likewise, one can show the set2T = {n2 + n | n ∈ N} = {0, 2, 6, 12, 20, ...} admits asimultaneous p-ordering. Thus

1!2T = (2− 0) = 2

2!2T = (6− 0)(6− 2) = 24

3!2T = (12− 0)(12− 2)(12− 6) = 720

4!2T = (20− 0)(20− 2)(20− 6)(20− 12) = 40320

n!2T = (2n)!

Michael R. Pilla Generalizations of the Factorial Function

Page 31: Generalized Factorials and Taylor Expansionscourse1.winona.edu/eerrthum/UndergradResearch/... · Generalized Factorials and Taylor Expansions Michael R. Pilla Winona State University

Factorials Examples Taylor Series Expansions Extensions

Twice Triangulars (Squares Modified)

Example

Likewise, one can show the set2T = {n2 + n | n ∈ N} = {0, 2, 6, 12, 20, ...} admits asimultaneous p-ordering. Thus

1!2T = (2− 0) = 2

2!2T = (6− 0)(6− 2) = 24

3!2T = (12− 0)(12− 2)(12− 6) = 720

4!2T = (20− 0)(20− 2)(20− 6)(20− 12) = 40320

n!2T = (2n)!

Michael R. Pilla Generalizations of the Factorial Function

Page 32: Generalized Factorials and Taylor Expansionscourse1.winona.edu/eerrthum/UndergradResearch/... · Generalized Factorials and Taylor Expansions Michael R. Pilla Winona State University

Factorials Examples Taylor Series Expansions Extensions

Twice Triangulars (Squares Modified)

Example

Likewise, one can show the set2T = {n2 + n | n ∈ N} = {0, 2, 6, 12, 20, ...} admits asimultaneous p-ordering. Thus

1!2T = (2− 0) = 2

2!2T = (6− 0)(6− 2) = 24

3!2T = (12− 0)(12− 2)(12− 6) = 720

4!2T = (20− 0)(20− 2)(20− 6)(20− 12) = 40320

n!2T = (2n)!

Michael R. Pilla Generalizations of the Factorial Function

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Factorials Examples Taylor Series Expansions Extensions

Twice Triangulars (Squares Modified)

Example

Likewise, one can show the set2T = {n2 + n | n ∈ N} = {0, 2, 6, 12, 20, ...} admits asimultaneous p-ordering. Thus

1!2T = (2− 0) = 2

2!2T = (6− 0)(6− 2) = 24

3!2T = (12− 0)(12− 2)(12− 6) = 720

4!2T = (20− 0)(20− 2)(20− 6)(20− 12) = 40320

n!2T = (2n)!

Michael R. Pilla Generalizations of the Factorial Function

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Factorials Examples Taylor Series Expansions Extensions

Twice Triangulars (Squares Modified)

Example

Likewise, one can show the set2T = {n2 + n | n ∈ N} = {0, 2, 6, 12, 20, ...} admits asimultaneous p-ordering. Thus

1!2T = (2− 0) = 2

2!2T = (6− 0)(6− 2) = 24

3!2T = (12− 0)(12− 2)(12− 6) = 720

4!2T = (20− 0)(20− 2)(20− 6)(20− 12) = 40320

n!2T = (2n)!

Michael R. Pilla Generalizations of the Factorial Function

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Factorials Examples Taylor Series Expansions Extensions

A Geometric Progression

Example

Consider the geometric progressionG = {5 · 3n} = {5, 15, 45, 135, 405, ...}. This set admits asimultaneous p-ordering and thus

1!G = (15− 5) = 10

2!G = (45− 5)(45− 15) = 1200

3!G = (135− 5)(135− 15)(135− 45) = 1404000

4!G = (405−5)(405−15)(405−45)(405−135) = 15163200000

Michael R. Pilla Generalizations of the Factorial Function

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Factorials Examples Taylor Series Expansions Extensions

A Geometric Progression

Example

Consider the geometric progressionG = {5 · 3n} = {5, 15, 45, 135, 405, ...}. This set admits asimultaneous p-ordering and thus

1!G = (15− 5) = 10

2!G = (45− 5)(45− 15) = 1200

3!G = (135− 5)(135− 15)(135− 45) = 1404000

4!G = (405−5)(405−15)(405−45)(405−135) = 15163200000

Michael R. Pilla Generalizations of the Factorial Function

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Factorials Examples Taylor Series Expansions Extensions

A Geometric Progression

Example

Consider the geometric progressionG = {5 · 3n} = {5, 15, 45, 135, 405, ...}. This set admits asimultaneous p-ordering and thus

1!G = (15− 5) = 10

2!G = (45− 5)(45− 15) = 1200

3!G = (135− 5)(135− 15)(135− 45) = 1404000

4!G = (405−5)(405−15)(405−45)(405−135) = 15163200000

Michael R. Pilla Generalizations of the Factorial Function

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Factorials Examples Taylor Series Expansions Extensions

A Geometric Progression

Example

Consider the geometric progressionG = {5 · 3n} = {5, 15, 45, 135, 405, ...}. This set admits asimultaneous p-ordering and thus

1!G = (15− 5) = 10

2!G = (45− 5)(45− 15) = 1200

3!G = (135− 5)(135− 15)(135− 45) = 1404000

4!G = (405−5)(405−15)(405−45)(405−135) = 15163200000

Michael R. Pilla Generalizations of the Factorial Function

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Factorials Examples Taylor Series Expansions Extensions

A Geometric Progression

Example

Consider the geometric progressionG = {5 · 3n} = {5, 15, 45, 135, 405, ...}. This set admits asimultaneous p-ordering and thus

1!G = (15− 5) = 10

2!G = (45− 5)(45− 15) = 1200

3!G = (135− 5)(135− 15)(135− 45) = 1404000

4!G = (405−5)(405−15)(405−45)(405−135) = 15163200000

Michael R. Pilla Generalizations of the Factorial Function

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Factorials Examples Taylor Series Expansions Extensions

A General Geometric Progression

Example

The geometric progression aqN gives a simultaneous p-ordering.Thus

n!aqN = (aqn − a)(aqn − aq) · · · (aqn − aqn−1)

= anqn(1− q−n)(1− q1−n) · · · (1− q−2)(1− q−1))

= (−aq)nq−n(n+1)

2 (1− q)(1− q2) · · · (1− qn)

= (−aq)nq−n(n+1)

2 (q : q)n

where (q : q)n is the q-Pochhammer symbol.

Michael R. Pilla Generalizations of the Factorial Function

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Factorials Examples Taylor Series Expansions Extensions

A General Geometric Progression

Example

The geometric progression aqN gives a simultaneous p-ordering.Thus

n!aqN = (aqn − a)(aqn − aq) · · · (aqn − aqn−1)

= anqn(1− q−n)(1− q1−n) · · · (1− q−2)(1− q−1))

= (−aq)nq−n(n+1)

2 (1− q)(1− q2) · · · (1− qn)

= (−aq)nq−n(n+1)

2 (q : q)n

where (q : q)n is the q-Pochhammer symbol.

Michael R. Pilla Generalizations of the Factorial Function

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Factorials Examples Taylor Series Expansions Extensions

A General Geometric Progression

Example

The geometric progression aqN gives a simultaneous p-ordering.Thus

n!aqN = (aqn − a)(aqn − aq) · · · (aqn − aqn−1)

= anqn(1− q−n)(1− q1−n) · · · (1− q−2)(1− q−1))

= (−aq)nq−n(n+1)

2 (1− q)(1− q2) · · · (1− qn)

= (−aq)nq−n(n+1)

2 (q : q)n

where (q : q)n is the q-Pochhammer symbol.

Michael R. Pilla Generalizations of the Factorial Function

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Factorials Examples Taylor Series Expansions Extensions

A General Geometric Progression

Example

The geometric progression aqN gives a simultaneous p-ordering.Thus

n!aqN = (aqn − a)(aqn − aq) · · · (aqn − aqn−1)

= anqn(1− q−n)(1− q1−n) · · · (1− q−2)(1− q−1))

= (−aq)nq−n(n+1)

2 (1− q)(1− q2) · · · (1− qn)

= (−aq)nq−n(n+1)

2 (q : q)n

where (q : q)n is the q-Pochhammer symbol.

Michael R. Pilla Generalizations of the Factorial Function

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Factorials Examples Taylor Series Expansions Extensions

A General Geometric Progression

Example

The geometric progression aqN gives a simultaneous p-ordering.Thus

n!aqN = (aqn − a)(aqn − aq) · · · (aqn − aqn−1)

= anqn(1− q−n)(1− q1−n) · · · (1− q−2)(1− q−1))

= (−aq)nq−n(n+1)

2 (1− q)(1− q2) · · · (1− qn)

= (−aq)nq−n(n+1)

2 (q : q)n

where (q : q)n is the q-Pochhammer symbol.

Michael R. Pilla Generalizations of the Factorial Function

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Factorials Examples Taylor Series Expansions Extensions

Non-Simultaneous Sets

Example

While it can be shown that the primes do NOT admit asimultaneous p-ordering, Bhargava gives an intricate formulato calculate them.

n!P =∏

p

pb n−1

p−1c+b n−1

p(p−1)c+b n−1

p2(p−1)c+···

{n!P} = {1, 2, 24, 48, 5670, ...}

Example

The set of cubes N3 does not admit a simultaneous p-orderingand has no nice formula.

{n!N3} = {1, 2, 504, 504, 35280, ...}

Michael R. Pilla Generalizations of the Factorial Function

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Factorials Examples Taylor Series Expansions Extensions

Non-Simultaneous Sets

Example

While it can be shown that the primes do NOT admit asimultaneous p-ordering, Bhargava gives an intricate formulato calculate them.

n!P =∏

p

pb n−1

p−1c+b n−1

p(p−1)c+b n−1

p2(p−1)c+···

{n!P} = {1, 2, 24, 48, 5670, ...}

Example

The set of cubes N3 does not admit a simultaneous p-orderingand has no nice formula.

{n!N3} = {1, 2, 504, 504, 35280, ...}

Michael R. Pilla Generalizations of the Factorial Function

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Factorials Examples Taylor Series Expansions Extensions

Non-Simultaneous Sets

Example

While it can be shown that the primes do NOT admit asimultaneous p-ordering, Bhargava gives an intricate formulato calculate them.

n!P =∏

p

pb n−1

p−1c+b n−1

p(p−1)c+b n−1

p2(p−1)c+···

{n!P} = {1, 2, 24, 48, 5670, ...}

Example

The set of cubes N3 does not admit a simultaneous p-orderingand has no nice formula.

{n!N3} = {1, 2, 504, 504, 35280, ...}

Michael R. Pilla Generalizations of the Factorial Function

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Factorials Examples Taylor Series Expansions Extensions

Non-Simultaneous Sets

Example

While it can be shown that the primes do NOT admit asimultaneous p-ordering, Bhargava gives an intricate formulato calculate them.

n!P =∏

p

pb n−1

p−1c+b n−1

p(p−1)c+b n−1

p2(p−1)c+···

{n!P} = {1, 2, 24, 48, 5670, ...}

Example

The set of cubes N3 does not admit a simultaneous p-orderingand has no nice formula.

{n!N3} = {1, 2, 504, 504, 35280, ...}

Michael R. Pilla Generalizations of the Factorial Function

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Factorials Examples Taylor Series Expansions Extensions

Non-Simultaneous Sets

Example

While it can be shown that the primes do NOT admit asimultaneous p-ordering, Bhargava gives an intricate formulato calculate them.

n!P =∏

p

pb n−1

p−1c+b n−1

p(p−1)c+b n−1

p2(p−1)c+···

{n!P} = {1, 2, 24, 48, 5670, ...}

Example

The set of cubes N3 does not admit a simultaneous p-orderingand has no nice formula.

{n!N3} = {1, 2, 504, 504, 35280, ...}

Michael R. Pilla Generalizations of the Factorial Function

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Factorials Examples Taylor Series Expansions Extensions

Summary of Examples

N ! n!N = n!

aN + b ! n!aN+b = ann!

2T ! n!2T = (2n)!

Z2 ! n!Z2 = (2n)!2

aqN ! n!aqN = (−aq)nq−n(n+1)

2 (q : q)n

P ! n!P =∏

p p(stuff )

Michael R. Pilla Generalizations of the Factorial Function

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Factorials Examples Taylor Series Expansions Extensions

Summary of Examples

N ! n!N = n!

aN + b ! n!aN+b = ann!

2T ! n!2T = (2n)!

Z2 ! n!Z2 = (2n)!2

aqN ! n!aqN = (−aq)nq−n(n+1)

2 (q : q)n

P ! n!P =∏

p p(stuff )

Michael R. Pilla Generalizations of the Factorial Function

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Factorials Examples Taylor Series Expansions Extensions

Summary of Examples

N ! n!N = n!

aN + b ! n!aN+b = ann!

2T ! n!2T = (2n)!

Z2 ! n!Z2 = (2n)!2

aqN ! n!aqN = (−aq)nq−n(n+1)

2 (q : q)n

P ! n!P =∏

p p(stuff )

Michael R. Pilla Generalizations of the Factorial Function

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Factorials Examples Taylor Series Expansions Extensions

Summary of Examples

N ! n!N = n!

aN + b ! n!aN+b = ann!

2T ! n!2T = (2n)!

Z2 ! n!Z2 = (2n)!2

aqN ! n!aqN = (−aq)nq−n(n+1)

2 (q : q)n

P ! n!P =∏

p p(stuff )

Michael R. Pilla Generalizations of the Factorial Function

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Factorials Examples Taylor Series Expansions Extensions

Summary of Examples

N ! n!N = n!

aN + b ! n!aN+b = ann!

2T ! n!2T = (2n)!

Z2 ! n!Z2 = (2n)!2

aqN ! n!aqN = (−aq)nq−n(n+1)

2 (q : q)n

P ! n!P =∏

p p(stuff )

Michael R. Pilla Generalizations of the Factorial Function

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Factorials Examples Taylor Series Expansions Extensions

Summary of Examples

N ! n!N = n!

aN + b ! n!aN+b = ann!

2T ! n!2T = (2n)!

Z2 ! n!Z2 = (2n)!2

aqN ! n!aqN = (−aq)nq−n(n+1)

2 (q : q)n

P ! n!P =∏

p p(stuff )

Michael R. Pilla Generalizations of the Factorial Function

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Factorials Examples Taylor Series Expansions Extensions

Question

Recall that one can write ex as a Taylor series. That is

ex =∞∑

n=0

xn

n!

Question: What is the !S -analogue to this equation?

As it turns out, this is the wrong question to ask.

Michael R. Pilla Generalizations of the Factorial Function

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Factorials Examples Taylor Series Expansions Extensions

Question

Recall that one can write ex as a Taylor series.

That is

ex =∞∑

n=0

xn

n!

Question: What is the !S -analogue to this equation?

As it turns out, this is the wrong question to ask.

Michael R. Pilla Generalizations of the Factorial Function

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Factorials Examples Taylor Series Expansions Extensions

Question

Recall that one can write ex as a Taylor series. That is

ex =∞∑

n=0

xn

n!

Question: What is the !S -analogue to this equation?

As it turns out, this is the wrong question to ask.

Michael R. Pilla Generalizations of the Factorial Function

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Factorials Examples Taylor Series Expansions Extensions

Question

Recall that one can write ex as a Taylor series. That is

ex =∞∑

n=0

xn

n!

Question: What is the !S -analogue to this equation?

As it turns out, this is the wrong question to ask.

Michael R. Pilla Generalizations of the Factorial Function

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Factorials Examples Taylor Series Expansions Extensions

Question

Recall that one can write ex as a Taylor series. That is

ex =∞∑

n=0

xn

n!

Question: What is the !S -analogue to this equation?

As it turns out, this is the wrong question to ask.

Michael R. Pilla Generalizations of the Factorial Function

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Factorials Examples Taylor Series Expansions Extensions

Right Question

Raising to the power of m, we can write (ex )m as follows:

(ex )m = emx =∞∑

n=0

mn

n!xn = 1 +

m

1!x +

m2

2!x2 +

m3

3!x3 + · · ·

Right Question: What is the !S -analogue of this equation?

Goal:

1) The numerator of each “coefficient” is a polynomial in m.

2) The denominator of each “coefficient” is a factorial.

Michael R. Pilla Generalizations of the Factorial Function

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Factorials Examples Taylor Series Expansions Extensions

Right Question

Raising to the power of m, we can write (ex )m as follows:

(ex )m = emx =∞∑

n=0

mn

n!xn = 1 +

m

1!x +

m2

2!x2 +

m3

3!x3 + · · ·

Right Question: What is the !S -analogue of this equation?

Goal:

1) The numerator of each “coefficient” is a polynomial in m.

2) The denominator of each “coefficient” is a factorial.

Michael R. Pilla Generalizations of the Factorial Function

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Factorials Examples Taylor Series Expansions Extensions

Right Question

Raising to the power of m, we can write (ex )m as follows:

(ex )m = emx =∞∑

n=0

mn

n!xn = 1 +

m

1!x +

m2

2!x2 +

m3

3!x3 + · · ·

Right Question: What is the !S -analogue of this equation?

Goal:

1) The numerator of each “coefficient” is a polynomial in m.

2) The denominator of each “coefficient” is a factorial.

Michael R. Pilla Generalizations of the Factorial Function

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Factorials Examples Taylor Series Expansions Extensions

Right Question

Raising to the power of m, we can write (ex )m as follows:

(ex )m = emx =∞∑

n=0

mn

n!xn = 1 +

m

1!x +

m2

2!x2 +

m3

3!x3 + · · ·

Right Question: What is the !S -analogue of this equation?

Goal:

1) The numerator of each “coefficient” is a polynomial in m.

2) The denominator of each “coefficient” is a factorial.

Michael R. Pilla Generalizations of the Factorial Function

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Factorials Examples Taylor Series Expansions Extensions

(aN+ b) -analogue

Example

( aa−x )m = (1− x

a )−m

= 1 + ma x + m(m−1)

2a2x2 + m(m−1)(m−2)

6a3x3

+ m(m−1)(m−2)(m−3)24a4

x4 + m(m−1)(m−2)(m−3)(m−4)120a5

x5 + · · ·

=∑∞

n=0PaN+b,n(m)

n!aN+bxn

Notice our numerators are polynomials in m and our denominatorsare ann! = n!aN+b.

Michael R. Pilla Generalizations of the Factorial Function

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Factorials Examples Taylor Series Expansions Extensions

(aN+ b) -analogue

Example

( aa−x )m = (1− x

a )−m

= 1 + ma x + m(m−1)

2a2x2 + m(m−1)(m−2)

6a3x3

+ m(m−1)(m−2)(m−3)24a4

x4 + m(m−1)(m−2)(m−3)(m−4)120a5

x5 + · · ·

=∑∞

n=0PaN+b,n(m)

n!aN+bxn

Notice our numerators are polynomials in m and our denominatorsare ann! = n!aN+b.

Michael R. Pilla Generalizations of the Factorial Function

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Factorials Examples Taylor Series Expansions Extensions

(aN+ b) -analogue

Example

( aa−x )m = (1− x

a )−m

= 1 + ma x + m(m−1)

2a2x2 + m(m−1)(m−2)

6a3x3

+ m(m−1)(m−2)(m−3)24a4

x4 + m(m−1)(m−2)(m−3)(m−4)120a5

x5 + · · ·

=∑∞

n=0PaN+b,n(m)

n!aN+bxn

Notice our numerators are polynomials in m and our denominatorsare ann! = n!aN+b.

Michael R. Pilla Generalizations of the Factorial Function

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Factorials Examples Taylor Series Expansions Extensions

(aN+ b) -analogue

Example

( aa−x )m = (1− x

a )−m

= 1 + ma x + m(m−1)

2a2x2 + m(m−1)(m−2)

6a3x3

+ m(m−1)(m−2)(m−3)24a4

x4 + m(m−1)(m−2)(m−3)(m−4)120a5

x5 + · · ·

=∑∞

n=0PaN+b,n(m)

n!aN+bxn

Notice our numerators are polynomials in m and our denominatorsare ann! = n!aN+b.

Michael R. Pilla Generalizations of the Factorial Function

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Factorials Examples Taylor Series Expansions Extensions

2T -analogue

Example

cosm(√x) =

1− m2 x + m+3m(m−1)

24 x2

−15m(m−1)+m+15m(m−1)(m−2)720 x3 + · · ·

=∑∞

n=0P2T,n(m)

n!2Txn

Note that by allowing multiplication by scalars, the Z2-analogue is

2cosm(√x) =

∞∑n=0

PZ2,n(m)

n!Z2

xn.

Michael R. Pilla Generalizations of the Factorial Function

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Factorials Examples Taylor Series Expansions Extensions

2T -analogue

Example

cosm(√x) = 1− m

2 x + m+3m(m−1)24 x2

−15m(m−1)+m+15m(m−1)(m−2)720 x3 + · · ·

=∑∞

n=0P2T,n(m)

n!2Txn

Note that by allowing multiplication by scalars, the Z2-analogue is

2cosm(√x) =

∞∑n=0

PZ2,n(m)

n!Z2

xn.

Michael R. Pilla Generalizations of the Factorial Function

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Factorials Examples Taylor Series Expansions Extensions

2T -analogue

Example

cosm(√x) = 1− m

2 x + m+3m(m−1)24 x2

−15m(m−1)+m+15m(m−1)(m−2)720 x3 + · · ·

=∑∞

n=0P2T,n(m)

n!2Txn

Note that by allowing multiplication by scalars, the Z2-analogue is

2cosm(√x) =

∞∑n=0

PZ2,n(m)

n!Z2

xn.

Michael R. Pilla Generalizations of the Factorial Function

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Factorials Examples Taylor Series Expansions Extensions

2T -analogue

Example

cosm(√x) = 1− m

2 x + m+3m(m−1)24 x2

−15m(m−1)+m+15m(m−1)(m−2)720 x3 + · · ·

=∑∞

n=0P2T,n(m)

n!2Txn

Note that by allowing multiplication by scalars, the Z2-analogue is

2cosm(√x) =

∞∑n=0

PZ2,n(m)

n!Z2

xn.

Michael R. Pilla Generalizations of the Factorial Function

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Factorials Examples Taylor Series Expansions Extensions

P -analogue

Example

(− ln(1− x)

x

)m

= 1 + m2 x + m(3m+5)

24 x2 + m(m2+5m+6)48 x3 + · · ·

=∞∑

n=0

PP,n(m)

n!Pxn

Notice that the coefficients in the denominator seem to be thesame as the factorials for the set of primes.

It turns out that this is so (Chabert, 2005).

Michael R. Pilla Generalizations of the Factorial Function

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Factorials Examples Taylor Series Expansions Extensions

P -analogue

Example

(− ln(1− x)

x

)m

= 1 + m2 x + m(3m+5)

24 x2 + m(m2+5m+6)48 x3 + · · ·

=∞∑

n=0

PP,n(m)

n!Pxn

Notice that the coefficients in the denominator seem to be thesame as the factorials for the set of primes.

It turns out that this is so (Chabert, 2005).

Michael R. Pilla Generalizations of the Factorial Function

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Factorials Examples Taylor Series Expansions Extensions

P -analogue

Example

(− ln(1− x)

x

)m

= 1 + m2 x + m(3m+5)

24 x2 + m(m2+5m+6)48 x3 + · · ·

=∞∑

n=0

PP,n(m)

n!Pxn

Notice that the coefficients in the denominator seem to be thesame as the factorials for the set of primes.

It turns out that this is so (Chabert, 2005).

Michael R. Pilla Generalizations of the Factorial Function

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Factorials Examples Taylor Series Expansions Extensions

Summary of !S-analogues

N ! n!N = n! !

(ex )m

aN + b ! n!aN+b = ann! !

( aa−x )m

2T ! n!2T = (2n)! !

cosm(√x)

Z2 ! n!Z2 = (2n)!2 !

2cosm(√x)

aqN ! n!aqN = (−aq)nq−n(n+1)

2 (q : q)n !

?

P ! n!P =∏

p p(stuff ) !

(− ln(1−x)

x

)m

? ! n!? ! (tan−1(x))m

Michael R. Pilla Generalizations of the Factorial Function

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Factorials Examples Taylor Series Expansions Extensions

Summary of !S-analogues

N ! n!N = n! ! (ex )m

aN + b ! n!aN+b = ann! !

( aa−x )m

2T ! n!2T = (2n)! !

cosm(√x)

Z2 ! n!Z2 = (2n)!2 !

2cosm(√x)

aqN ! n!aqN = (−aq)nq−n(n+1)

2 (q : q)n !

?

P ! n!P =∏

p p(stuff ) !

(− ln(1−x)

x

)m

? ! n!? ! (tan−1(x))m

Michael R. Pilla Generalizations of the Factorial Function

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Factorials Examples Taylor Series Expansions Extensions

Summary of !S-analogues

N ! n!N = n! ! (ex )m

aN + b ! n!aN+b = ann! ! ( aa−x )m

2T ! n!2T = (2n)! !

cosm(√x)

Z2 ! n!Z2 = (2n)!2 !

2cosm(√x)

aqN ! n!aqN = (−aq)nq−n(n+1)

2 (q : q)n !

?

P ! n!P =∏

p p(stuff ) !

(− ln(1−x)

x

)m

? ! n!? ! (tan−1(x))m

Michael R. Pilla Generalizations of the Factorial Function

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Factorials Examples Taylor Series Expansions Extensions

Summary of !S-analogues

N ! n!N = n! ! (ex )m

aN + b ! n!aN+b = ann! ! ( aa−x )m

2T ! n!2T = (2n)! ! cosm(√x)

Z2 ! n!Z2 = (2n)!2 !

2cosm(√x)

aqN ! n!aqN = (−aq)nq−n(n+1)

2 (q : q)n !

?

P ! n!P =∏

p p(stuff ) !

(− ln(1−x)

x

)m

? ! n!? ! (tan−1(x))m

Michael R. Pilla Generalizations of the Factorial Function

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Factorials Examples Taylor Series Expansions Extensions

Summary of !S-analogues

N ! n!N = n! ! (ex )m

aN + b ! n!aN+b = ann! ! ( aa−x )m

2T ! n!2T = (2n)! ! cosm(√x)

Z2 ! n!Z2 = (2n)!2 ! 2cosm(

√x)

aqN ! n!aqN = (−aq)nq−n(n+1)

2 (q : q)n !

?

P ! n!P =∏

p p(stuff ) !

(− ln(1−x)

x

)m

? ! n!? ! (tan−1(x))m

Michael R. Pilla Generalizations of the Factorial Function

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Factorials Examples Taylor Series Expansions Extensions

Summary of !S-analogues

N ! n!N = n! ! (ex )m

aN + b ! n!aN+b = ann! ! ( aa−x )m

2T ! n!2T = (2n)! ! cosm(√x)

Z2 ! n!Z2 = (2n)!2 ! 2cosm(

√x)

aqN ! n!aqN = (−aq)nq−n(n+1)

2 (q : q)n !

?

P ! n!P =∏

p p(stuff ) !

(− ln(1−x)

x

)m

? ! n!? ! (tan−1(x))m

Michael R. Pilla Generalizations of the Factorial Function

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Factorials Examples Taylor Series Expansions Extensions

Summary of !S-analogues

N ! n!N = n! ! (ex )m

aN + b ! n!aN+b = ann! ! ( aa−x )m

2T ! n!2T = (2n)! ! cosm(√x)

Z2 ! n!Z2 = (2n)!2 ! 2cosm(

√x)

aqN ! n!aqN = (−aq)nq−n(n+1)

2 (q : q)n ! ?

P ! n!P =∏

p p(stuff ) !

(− ln(1−x)

x

)m

? ! n!? ! (tan−1(x))m

Michael R. Pilla Generalizations of the Factorial Function

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Factorials Examples Taylor Series Expansions Extensions

Summary of !S-analogues

N ! n!N = n! ! (ex )m

aN + b ! n!aN+b = ann! ! ( aa−x )m

2T ! n!2T = (2n)! ! cosm(√x)

Z2 ! n!Z2 = (2n)!2 ! 2cosm(

√x)

aqN ! n!aqN = (−aq)nq−n(n+1)

2 (q : q)n ! ?

P ! n!P =∏

p p(stuff ) !

(− ln(1−x)

x

)m

? ! n!? !

(tan−1(x))m

Michael R. Pilla Generalizations of the Factorial Function

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Factorials Examples Taylor Series Expansions Extensions

Summary of !S-analogues

N ! n!N = n! ! (ex )m

aN + b ! n!aN+b = ann! ! ( aa−x )m

2T ! n!2T = (2n)! ! cosm(√x)

Z2 ! n!Z2 = (2n)!2 ! 2cosm(

√x)

aqN ! n!aqN = (−aq)nq−n(n+1)

2 (q : q)n ! ?

P ! n!P =∏

p p(stuff ) !

(− ln(1−x)

x

)m

? ! n!? ! (tan−1(x))m

Michael R. Pilla Generalizations of the Factorial Function

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Factorials Examples Taylor Series Expansions Extensions

Future Work

Conjecture A

Every subset of N corresponds to a function.Issues:

They probably won’t be classical functions.

Difficulty: Finding the correct polynomials in the numerator.

Is it theoretically useful to allow for constants such as for Z2?

Conjecture B

Every analytic function

(with conditions?)

corresponds to a subsetof N.Issues:

What are the conditions?

Michael R. Pilla Generalizations of the Factorial Function

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Factorials Examples Taylor Series Expansions Extensions

Future Work

Conjecture A

Every subset of N corresponds to a function.

Issues:

They probably won’t be classical functions.

Difficulty: Finding the correct polynomials in the numerator.

Is it theoretically useful to allow for constants such as for Z2?

Conjecture B

Every analytic function

(with conditions?)

corresponds to a subsetof N.

Issues:

What are the conditions?

Michael R. Pilla Generalizations of the Factorial Function

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Factorials Examples Taylor Series Expansions Extensions

Future Work

Conjecture A

Every subset of N corresponds to a function.Issues:

They probably won’t be classical functions.

Difficulty: Finding the correct polynomials in the numerator.

Is it theoretically useful to allow for constants such as for Z2?

Conjecture B

Every analytic function

(with conditions?)

corresponds to a subsetof N.

Issues:

What are the conditions?

Michael R. Pilla Generalizations of the Factorial Function

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Factorials Examples Taylor Series Expansions Extensions

Future Work

Conjecture A

Every subset of N corresponds to a function.Issues:

They probably won’t be classical functions.

Difficulty: Finding the correct polynomials in the numerator.

Is it theoretically useful to allow for constants such as for Z2?

Conjecture B

Every analytic function

(with conditions?)

corresponds to a subsetof N.

Issues:

What are the conditions?

Michael R. Pilla Generalizations of the Factorial Function

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Factorials Examples Taylor Series Expansions Extensions

Future Work

Conjecture A

Every subset of N corresponds to a function.Issues:

They probably won’t be classical functions.

Difficulty: Finding the correct polynomials in the numerator.

Is it theoretically useful to allow for constants such as for Z2?

Conjecture B

Every analytic function

(with conditions?)

corresponds to a subsetof N.

Issues:

What are the conditions?

Michael R. Pilla Generalizations of the Factorial Function

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Factorials Examples Taylor Series Expansions Extensions

Future Work

Conjecture A

Every subset of N corresponds to a function.Issues:

They probably won’t be classical functions.

Difficulty: Finding the correct polynomials in the numerator.

Is it theoretically useful to allow for constants such as for Z2?

Conjecture B

Every analytic function

(with conditions?)

corresponds to a subsetof N.

Issues:

What are the conditions?

Michael R. Pilla Generalizations of the Factorial Function

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Factorials Examples Taylor Series Expansions Extensions

Future Work

Conjecture A

Every subset of N corresponds to a function.Issues:

They probably won’t be classical functions.

Difficulty: Finding the correct polynomials in the numerator.

Is it theoretically useful to allow for constants such as for Z2?

Conjecture B

Every analytic function

(with conditions?)

corresponds to a subsetof N.Issues:

What are the conditions?

Michael R. Pilla Generalizations of the Factorial Function

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Factorials Examples Taylor Series Expansions Extensions

Future Work

Conjecture A

Every subset of N corresponds to a function.Issues:

They probably won’t be classical functions.

Difficulty: Finding the correct polynomials in the numerator.

Is it theoretically useful to allow for constants such as for Z2?

Conjecture B

Every analytic function (with conditions?) corresponds to a subsetof N.Issues:

What are the conditions?

Michael R. Pilla Generalizations of the Factorial Function

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Factorials Examples Taylor Series Expansions Extensions

Future Work

Conjecture A

Every subset of N corresponds to a function.Issues:

They probably won’t be classical functions.

Difficulty: Finding the correct polynomials in the numerator.

Is it theoretically useful to allow for constants such as for Z2?

Conjecture B

Every analytic function (with conditions?) corresponds to a subsetof N.Issues:

What are the conditions?

Michael R. Pilla Generalizations of the Factorial Function

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Factorials Examples Taylor Series Expansions Extensions

If The Conjectures Are True...

−a ln(a− x) // ?

a

a− x

∫dx

OO

//

ddx

��

aN + boo

a

(a− x)2// ?

Michael R. Pilla Generalizations of the Factorial Function

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Factorials Examples Taylor Series Expansions Extensions

Thanks

References

Bhargava, M. (2000). The factorial function andgeneralizations. The American Mathematical Monthly,107(9), 783-799.

Chabert, J.L. (2007). Integer-valued polynomials on primenumbers and logarithm power expansion. EuropeanJournal of Combinatorics, 28(3), 754-761.

Thanks Professor Eric Errthum!

Questions

Michael R. Pilla Generalizations of the Factorial Function

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Factorials Examples Taylor Series Expansions Extensions

Thanks

References

Bhargava, M. (2000). The factorial function andgeneralizations. The American Mathematical Monthly,107(9), 783-799.

Chabert, J.L. (2007). Integer-valued polynomials on primenumbers and logarithm power expansion. EuropeanJournal of Combinatorics, 28(3), 754-761.

Thanks Professor Eric Errthum!

Questions

Michael R. Pilla Generalizations of the Factorial Function

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Factorials Examples Taylor Series Expansions Extensions

Thanks

References

Bhargava, M. (2000). The factorial function andgeneralizations. The American Mathematical Monthly,107(9), 783-799.

Chabert, J.L. (2007). Integer-valued polynomials on primenumbers and logarithm power expansion. EuropeanJournal of Combinatorics, 28(3), 754-761.

Thanks Professor Eric Errthum!

Questions

Michael R. Pilla Generalizations of the Factorial Function