First you need to know some **IMPORTANT rules** about the prime numbers. Some of them:

1. A prime number can be divided, without a remainder, only by itself and by 1. For example, 17 can be divided only by 17 and by 1.

2. The only even prime number is 2. All other even numbers can be divided by 2.

3. Zero and 1 are not considered prime numbers.

4. To prove whether a number is a prime number, first try dividing it by 2, and see if you get a whole number. If you do, it can't be a prime number. If you don't get a whole number, next try dividing it by prime numbers: 3, 5, 7, 11 (9 is divisible by 3) and so on, always dividing by a prime number.