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TheSchoolRun.com closure date

As we informed you a few months ago, TheSchoolRun has had to make the difficult decision to close due to financial pressures and the company has now ceased trading. We had hoped to keep our content available through a partnership with another educational provider, but this provider has since withdrawn from the agreement.

As a result, we now have to permanently close TheSchoolRun.com. However, to give subscribers time to download any content they’d like to keep, we will keep the website open until 31st July 2025. After this date, the site will be taken down and there will be no further access to any resources. We strongly encourage you to download and save any resources you think you may want to use in the future.

In particular, we suggest downloading:

You should already have received 16 primary school eBooks (worth £108.84) to download and keep. If you haven’t received these, please contact us at [email protected] before 31st July 2025, and we will send them to you.

We are very sorry that there is no way to continue offering access to resources and sincerely apologise for the inconvenience caused.

What is a prime number?

Prime numbers
We explain what prime numbers are and give examples of the types of questions KS2 children might be asked to test their knowledge of prime numbers.

What is a prime number?

A prime number is a number greater than 1 that cannot be divided evenly by any number other than itself or 1.

For example: 17 is a prime number because you cannot divide it (without a remainder) by any number except 17 or 1:

17 ÷ 17 = 1

17 ÷ 1 = 17

Prime numbers in Key Stage 2

Children in Years 5 and 6 are expected to recall prime numbers up to 19 and establish whether numbers above that, up to 100, are prime. Here are all the prime numbers under 100: 

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

They may be asked questions such as the following to test them on their knowledge of prime numbers:

36 has two factors which are prime numbers. What are they?

Answer: 2 and 3

Sometimes questions on prime numbers will be combined with other skills, such as probability:

Susan has this spinner:

What is the probability that when Susan spins the spinner it will land on a prime number?

Answer: Since 3, 5, 7, 11 and 13 are prime numbers, the probability will be 5/6.

Prime number investigations

Prime numbers can be a fascinating subject. and they play a big role in modern business and our online life. Prime numbers are used to create the public key cryptography algorithms which are used to secure nearly all online data transfers, including email encryption and bank card security. Almost every online purchase made will use prime numbers in its security process!

Show your child the world's largest known prime number, which is over 17 million decimal digits long.