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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.

 


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