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MathNet 2008-part-01 — 165 problems (EN–VI) Question 95

Math Olympiad Vault · MathNet 2008-part-01 — 165 problems (EN–VI)

Question 95

Find all functions $f$ defined on the natural numbers that take values among the natural numbers for which
$$
(f(n))^{p} \equiv n \pmod{f(p)}
$$
for all $n \in \mathbf{N}$ and all prime numbers $p$.