Prime & Composite Numbers

3 and 7 are both prime numbers. 

7 can only be divided evenly by 1 or itself without a remainder, so it is a prime number

1 x 7  or  7 x 1

3 can only be divided evenly by 1 or itself without a remainder, so it is a prime number

1 x 3  or 3 x 1

6 is a composite number.

6 can be divided evenly by 1, 2, 3 and 6 so it is NOT a prime number

1 x 6   6 x 1   2 x 3   3 x 2

Click here to watch a helpful video.

Click here to practice with prime & composite numbers online.

Factor sets and can also be used to help determine if a number is prime or composite.

Factor sets are simply the sets of multiplication facts that can be used to create a particular number.  These can then be used to determine if a number is prime or composite.

Example:

The multiplication facts for 12 are

1 x 12     12 x 1     2 x 6     6 x 2   3 x 4    4 x 3

These factors can then be organized into a list or a T-chart.  Each factor will be listed only once.

List:  1, 2, 3, 4, 6, and 12

 T-chart: 

A number is composite if it can be made using factor sets other than one and itself, so 12 is a composite number.

Here are some more examples of factor sets listed in T-charts.