# Composite Numbers

**Composite number** is a number, that is not prime.

For example, 6 is composite number because its has other factors except 1 and 6, namely, 2 and 3.

By convention 1 is not composite.

This means that 1 is neither prime, nor composite.

**Example 1.** Determine whether 27 is composite.

Composite because 27 is divisible by 3, so 3 is factor of 27.

Next example.

**Example 2.** Determine whether 31 is composite.

It is prime number (not composite) because it has only two factors: 1 and 31.

Now, practice a bit.

**Exercise 1.** Determine whether 37 is composite.

**Answer**: not composite (prime).

Next exercise.

**Exercise 2.** Determine whether 121 is prime.

**Answer**: composite. Hint: 11 is a factor of 121.