Neocijenjeno
April 7, 2017, 10:51 p.m. (9 years, 5 months)
Let f be a non-constant function from the set of positive integers into the set of positive integer, such that a-b divides f\!\left(a\right)-f\!\left(b\right) for all distinct positive integers a, b. Prove that there exist infinitely many primes p such that p divides f\!\left(c\right) for some positive integer c.

Proposed by Juhan Aru, Estonia
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