# Prime Numbers

## What is a prime number?

A prime number is a whole number greater than 1 with only two factors - itself and 1. This means that it can only be divided by itself and 1, without remainders.

For example, 11 is a prime number because it can only be divided by 1 and 11. However, 12 is not a prime number because it can be divided by 1, 2, 3, 4, 6 and 12.

## Why is 1 not a prime number?

1 can only be divided by one number, itself. This means it has only one factor. By definition, prime numbers have exactly two factors.

## Are there any even prime numbers?

There is only one even prime number - 2. This is the only even number that has only two factors.

## Prime numbers to 100:

There are 25 prime numbers below 100.

They are: 2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89 and 97.

Download our FREE Prime Numbers to 100 Grid to use as a teaching aid or part of a display.

## How to find prime numbers from 1 - 100:

This is a fun, visual activity which allows children to find all of the prime numbers up to 100 easily. They will need a blank hundred square grid. Give the following instructions one at a time:

1. Cross off number 1. 1 is not a prime number as it only has one factor - itself.

2. 2 is a prime number, because it has exactly two factors - 1 and itself. However, you can cross off all of the multiples of 2 (other than 2, no even number is a prime number).

3. 3 is a prime number, because it has exactly two factors - 1 and itself. However, you can cross off all of the multiples of 3.

4. 5 is a prime number, because it has exactly two factors - 1 and itself. However, you can cross off all of the multiples of 5.

5. 7 is a prime number, because it has exactly two factors - 1 and itself. However, you can cross off all of the multiples of 7.

The numbers that are left on the grid are prime numbers.

## Prime numbers Year 5:

The concept of prime numbers is introduced to children in Year 5. In line with the national curriculum, they are expected to:

• know and use the vocabulary of prime numbers, prime factors and composite (nonprime) numbers
• establish whether a number up to 100 is prime and recall prime numbers up to 19

## Prime numbers Year 6:

Children develop their knowledge and understanding of prime numbers in Year 6. In line with the national curriculum, they are expected to:

• identify common factors, common multiples and prime numbers