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MathNet 2026 — Part 06 Question 56

Math Olympiad Vault · MathNet 2026 — Part 06

Question 56

Let $\mathbb{N}$ denote the strictly positive integers. A function $f : \mathbb{N} \to \mathbb{N}$ satisfies the following for all $n \in \mathbb{N}$:
$$
\begin{aligned}
f(1) &= 1 \\
f(f(n)) &= n \\
f(2n) &= 2f(n) + 1.
\end{aligned}
$$
Find the value of $f(2020)$.