olymmath

INMO 2023 Problem 1

    Let SS be a finite set of positive integers. Assume that there are precisely 2023 ordered pairs (x,y)(x, y) in S×SS \times S so that the product xyx y is a perfect square. Prove that one can find at least four distinct elements in SS so that none of their pairwise products is a perfect square.

    Note: As an example, if S={1,2,4}S=\{1,2,4\}, there are exactly five such ordered pairs: (1,1),(1,4)(1,1),(1,4), (2,2),(4,1)(2,2),(4,1), and (4,4)(4,4).

    Dataset text NuminaMath olympiads. Quoted with source.

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