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IMO 2015 — Complete Shortlist Question 24

IMO Shortlist · IMO 2015 — Complete Shortlist

Question 24

Let $m$ and $n$ be positive integers such that $m\gt n$. Define $x_{k}=(m+k) /(n+k)$ for $k=$ $1,2, \ldots, n+1$. Prove that if all the numbers $x_{1}, x_{2}, \ldots, x_{n+1}$ are integers, then $x_{1} x_{2} \cdots x_{n+1}-1$ is divisible by an odd prime.