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### 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 1 1 2 1 and 2 3 1 and 3 4 1, 2 and 4 5 1 and 5 6 1, 2, 3 and 6 7 1 and 7 8 1, 2, 4 and 8 9 1, 3 and 9 10 1, 2, 5 and 10 11 1 and 11 12 1, 2, 3, 4, 5 and 12 13 1 and 13 14 1, 2, 7 and 14 15 1, 3, 5 and 15 16 1, 2, 4, 8 and 16 17 1 and 17 18 1. 2, 3, 6, 9 and 18 19 1 and 19 20 1, 2, 4, 5, 10 and 20 21 1, 3, 7 and 21 22 1, 2, 11 and 22 23 1 and 23 24 1, 2, 3, 4, 6, 8, 12 and 24 25 1, 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.