**Prime Numbers and Prime Factorization**
**File: Interactive flash**
**Grade: 5-6**
**What are Factors?**
Factors are the numbers you multiply together to get a product.

Ex: The product 16 has several factors.

16 = 1 x 16

16 = 2 x 8

16 = 4 x 4

SO, the factors are 1, 2, 4, 8 and 16.

Let’s find the factors of 16.

**How to Get Factors**
Begin with 1 times the number 16.

1 x 16

Then, try 2, 3, 4, and so on…

2 x 8

3 x ? - 3 is not a factor, so cross it out

4 x 4

If you get doubles (like 4 x 4), then you’re done. Repeats or doubles means you’re finished.

The factors of 16 are 1, 2, 4, 8, 16

**Prime and Composite Numbers**
**Prime numbers** are numbers that only have two factors: one, and the number itself.

EXAMPLES:

3, 5, 7, 11, 31

**Composite numbers** have more than two factors.

EXAMPLES:

6, 15, 24, 30, 45

Remember this List of Prime Numbers up to 100. They can help in our lesson.

2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97

**Product of Primes**
Every composite number can be expressed as a product of prime numbers.

This is called prime factorization.

12 is a composite number.

It can be expressed as a product of primes: 2 x 2 x 3 or 22 x 3

**To find the prime factorization:**
Divide the number by the first prime number possible.

Circle the prime number, and continue with the other factor.

Divide the new factor by a prime number.

Continue this process until the only numbers you have left are prime numbers.

*For more about the lesson watch the flash presentation of* **Prime Numbers and Prime Factorization**