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YouTube Videos – Prime number and Related Articles

Demonstration, with Cuisenaire rods, that the number 7 is prime, being divisible only by 1 and 7

Plot of the zeta function ζ(s). At s=1, the function has a pole, that is to say, it tends to infinity.

Image: Ulam 2

The number 12 is not a prime, as 12 items can be placed into 3 equal-size columns of 4 each (among other ways). 11 items cannot be all placed into several equal-size columns of more than 1 item each without some extra items leftover (a remainder). Therefore, the number 11 is a prime.