Let's look at the rules for prime and composite numbers. All whole numbers that are greater than one can be classified as **prime** or **composite** numbers.

Prime numbers have only factors one and itself. A composite number has other factors other than itself and one. So let's look at some examples. Let's look at 4 and 5.

Four is divisible by 1 and four is divisible by 2 so four is a composite number.

Five is divisible by 1 but it is odd so it is not divisible by 2 or any other number so 5 is prime

So let's look at some that are a little bit larger. Let's look at thirty and thirty-one.

30 is divisible by 1

It is, even so, this means it is divisible by 2 so you already know it is composite.

But it also is divisible by 3 and 5.

So 30 is **composite.**

31 is divisible by 1

It is not divisible by 2 or 3 or any other number so it is prime.

Interesting fact, two is the only even prime number.

Any other number that is even will be a composite number because it is divisible by two.

So in summary,

Prime numbers are only divisible by two numbers 1 and itself.

Composite numbers are divisible by factors other than itself and one.

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