olymmath

BALTIC-WAY 2021 Problem 20

    Let n≥2n \geq 2 be an integer. Given numbers a1,a2,…,an∈{1,2,3,…,2n}a_{1}, a_{2}, \ldots, a_{n} \in\{1,2,3, \ldots, 2 n\} such that lcm⁡(ai,aj)>2n\operatorname{lcm}\left(a_{i}, a_{j}\right)>2 n for all 1≤i<j≤n1 \leq i<j \leq n, prove that

    a1a2⋯an∣(n+1)(n+2)⋯(2n−1)(2n).a_{1} a_{2} \cdots a_{n} \mid(n+1)(n+2) \cdots(2 n-1)(2 n) .

    Dataset text NuminaMath olympiads. Quoted with source.

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