Let P(x) be a non-constatnt polynomial whose coefficients are positive integers. If P(n) divides P(P(n) - 2015) for every natural number n, prove that P(- 2015) = 0.

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Note that P(n) - 2015 - (-2015) = P(n) divides P(P(n) - 2015) - P(-2015) for every  positive integer n. But P(n) divides P(P(n) - 2015) for every positive integer n. Therefore  P(n) divides P(-2015) for every positive integer n. Hence P(-2015) = 0.

Note  

In the original version of the problem the word 'non-constant' was missing. The  falsity of the statement was brought to the attention of the examiners by a  contestant who mentioned it in a remark at the end of a perfect solution to the  problem assuming that the polynomial is non-constant. Many students assumed  that the polynomial is non-constant and completed the solution. They deserved  full credit for doing so.

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