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