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MathNet 2013 Question 93

Math Olympiad Vault · MathNet 2013

Question 93

Let $A=\{1,2,3,\ldots,n\}$ with $n\gt 5$. Prove that there is a finite set B of distinct positive integers such that $A\subseteq B$ and
$$\prod_{x\in B}x=\sum_{x\in B}x^2.$$