Prime numbers are the numbers that has only two factors: 1 and number itself.

A composite number has more than two factors.

Prime numbers less than 20 are;

2, 3, 5, 7, 11, 13, 17 and 19.

Composite numbers less than 20 are;

4, 6, 8, 9, 10, 12, 14, 15, 16, and 18.

Note: Every Number that is not a prime number is a composite number.