Maths Olympiad Prep

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Number theory Difficulty 8.2 Shortlist Prove it Hong Kong

Find all positive integers nn with the following property: the kk positive divisors of nn have a permutation (d1,d2,,dk)(d_1, d_2, \dots, d_k) such that for every i=1,2,,ki = 1, 2, \dots, k, the number d1+d2++did_1 + d_2 + \dots + d_i is a perfect square.

Solution

2. (IMO Shortlist 2021 N3) See the official solution.

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