Prime numbers

A prime number is a whole number, greater than 1, that only has two factors.

A factor is a number that divides another number evenly, with no remainder or decimal.

The factors of a prime number are the number itself and 1.

19 is a prime number. It can only be divided by 1 and 19 without any remainders. The only factors of 19 are 1 and 19.

A number that has more than two factors is called a composite number.

The number 1 is not a prime number as it only has one factor.

Complete this interactive activity to find out about prime numbers. Then put your knowledge to the test.

Prime numbers are numbers that have only two factors: 1 and themselves.

Here are all the prime numbers up to 19:

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

Remember, 2 is the only even prime number, and 1 is not a prime number.

Working out if a number is a prime number

Ask these questions to work out if a number is prime:

1. Is it greater than 1?

If the answer is 'yes'. Then it could be a prime number.

2. Is it a whole number?

If the answer is 'yes'. It still could be a prime number.

3. Is it an odd number?

If the answer is 'yes'. It still might be a prime number. However, remember the number 2 is the only even prime number.

4. Is it a multiple of 5 or 10?

If the answer is 'no'. It could be a prime number.

5. Does it have any factors other than 1 or itself?

Use your multiplication facts and division skills to find out.

If the answer to this question is 'no', then it is a prime number!.

You can use a multiplication grid to help you.