### Prime number

A prime number has two divisors.

##### Explanation

You would expect that the larger the number, the more often you can divide it.

divisible by 11 21 and 2 31 and 3 41, 2 and 4 51 and 5 61, 2, 3 and 6 71 and 7 81, 2, 4 and 8 91, 3 and 9 101, 2, 5 and 10 111 and 11 121, 2, 3, 4, 5 and 12 131 and 13 141, 2, 7 and 14 151, 3, 5 and 15 161, 2, 4, 8 and 16 171 and 17 181. 2, 3, 6, 9 and 18 191 and 19 201, 2, 4, 5, 10 and 20 211, 3, 7 and 21 221, 2, 11 and 22 231 and 23 241, 2, 3, 4, 6, 8, 12 and 24 251, 5 and 25

The numbers 2, 3, 5, 7, 11, 13, 17, 19, 23 are only divisible by 1 or by itself. We call them prime numbers. We notice that all prime numbers are odd, with the exception of 2. That makes sense because you can divide all even numbers by 2, and they therefore do not qualify.

Our guess, that prime numbers will be further and further apart is not justified. Even in this small table you can already see that there are twin primes. Just look at 11 and 13, or at 17 and 19. Mathematicians like that and they have of course long been examining whether that always continues.