Prime and Composite Numbers

Prime Number

47 57

A Prime Number is a whole number greater than 1 that has exactly two factors, 1 and itself.

Which number is prime?

Composite Number

20Factors: 1, 2, 4, 5, 10, 20

55Factors: 1, 5, 11, 55

A composite number is a whole number greater than one that has more than two factors

108

9 12

3 3 4 3

3 3 2 2 3

Prime Factorization

Expressing a composite number as a product of prime numbers

2233 Rewrite as:

Method 1

Method 2: An easy way of keeping track of the factorization is to do upside-down division. It looks like this:

                   

The nice thing about this upside-down division is that, when you're done, the prime factorization is the product of all the numbers around the outside. The factors are circled in red above.

Try prime factorization on these composite numbers!!

64 36

144 972