2023 AMC 12A Problems/Problem 25

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Let $a$ and $b$ be positive integers such that $ab + 1$ divides $a^{2} + b^{2}$. Show that $\frac {a^{2} + b^{2}}{ab + 1}$ is the square of an integer.


This is totally this year's problem. Hmmmmmmm. Totally not that IMO question 6