olymmath

ISL 2021 N3

    Find all positive integers nn with the following property: the kk positive divisors of nn have a permutation (d1,d2,…,dk)\left(d_{1}, d_{2}, \ldots, d_{k}\right) such that for every i=1,2,…,ki=1,2, \ldots, k, the number d1+⋯+did_{1}+\cdots+d_{i} is a perfect square.

    Official text Transcription from NuminaMath olympiads, checked word for word against the official paper. Quoted with source.

    Official text: IMO 2021 Shortlist booklet, page 10.

    Solutions

    Official solution Solution 1 by the IMO Problem Selection Committee

    The terms of the source let olymmath link to this solution but not copy it. Read the solution (IMO official site).

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