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MathNet 2023-part-03 — 191 problems (EN–VI) Question 22

Math Olympiad Vault · MathNet 2023-part-03 — 191 problems (EN–VI)

Question 22

Let $g: \mathbb{N} \to \mathbb{N}$ be a bijective function and suppose that $f: \mathbb{N} \to \mathbb{N}$ is a function such that:
• For all naturals $x$, $f^{x^{2023}}(x) = x$
• For all naturals $x, y$ such that $x \mid y$, we have $f(x) \mid g(y)$.
Prove that $f(x) = x$.