Prime Squared

Let p p be a prime number , with p > 3 p > 3 . What is the greatest integer x x such that all p 2 p^{2} have a remainder of 1 when divided by x x ?


The answer is 24.

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1 solution

John Smith
Dec 22, 2016

Since p 2 p^{2} has a remainder of 1 1 when divided by x x , then x p 2 1 x | p^{2}-1 . p 2 1 p^{2}-1 = ( p 1 ) ( p + 1 ) (p-1)*(p+1) . p p is prime, so it is odd, given that the only even prime number is 2 and p > 3 p > 3 , so p 1 p-1 and p + 1 p+1 are even, and because they're consecutive even numbers, one of them is a multiple of 4 4 . Also, p p , p 1 p-1 and p + 1 p+1 are 3 3 consecutive integers, so one of them is a multiple of 3 3 and it can't be p p because it is prime and greater than 3 3 . Therefore 2 4 3 p 2 1 {2*4*3}|p^{2}-1 . So the answer is 24 24

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