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
$$\prod_{x\in B}x=\sum_{x\in B}x^2.$$
$$\prod_{x\in B}x=\sum_{x\in B}x^2.$$
Math Olympiad Vault · MathNet 2013