In other words, the prime number can be divided only by 1 and by itself.

Example: 5 is a prime number, because the only factors it has are 1 and 5.

A composite number has at least one more factor that the number itself or 1.

In fact, all whole numbers that are not prime are composite except for 1 and 0, which are not prime and not composite.

The composite numbers less than 20 are 4, 6, 8, 9, 10, 12, 14, 15, 16, 18