Prime numbers to 100
You learn about prime numbers: numbers only divisible by 1 and themselves.
How to work it out
- Try if the number is divisible by 2, 3, 5 or 7.
- If none go into it, then it has only two divisors: 1 and itself.
- Then it is a prime number.
1 × 7
A worked example
Is 7 a prime number?
- Can you divide 7 by 2, 3, 4, 5 or 6? No.
- Only by 1 and 7.
- So 7 is prime.
Another example
Is 12 a prime number?
- You can divide 12 by 2, 3, 4 and 6.
- So 12 is not prime.
Try it yourself
Answer with yes or no
Is 29 a prime number?
Answer with yes or no
Is 17 a prime number?
Watch out
You think an odd number is always a prime number: 51 and 91 look prime, but they aren’t.
Try 3 and 7 too. An odd number can still be in another times table.
You call 1 a prime number.
A prime number has two different factors. The number 1 has only one, so 1 is not a prime number.
Tips
- The first few prime numbers are: 2, 3, 5, 7, 11, 13, 17, 19, 23.
Why it works
A prime number cannot be split into equal groups (except groups of 1 or groups of itself). These special numbers are: 2, 3, 5, 7, 11, 13, 17, 19, 23 and so on.