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Product equals sum of squares

Source: 28th Iberoamerican Olympiad 2013, Problem 3

September 24, 2013
inductionnumber theory proposednumber theoryIberoamerican

Problem Statement

Let A={1,...,n}A = \{1,...,n\} with n \textgreater 5. Prove that one can find BB a finite set of positive integers such that AA is a subset of BB and
xBx2=xBx\displaystyle\sum_{x \in B} x^2 = \displaystyle\prod_{x \in B} x