ILL 1987 Problem 74

Does there exist a function $f : \mathbb N \to \mathbb N$ , such that $f(f(n)) =n + 1987$ for every natural number $n$ ? (IMO Problem 4)

Proposed by Vietnam.

Dataset text AoPS wiki problems. Quoted with source.

Solutions

No solution is on olymmath yet. Official and human solutions come first when they arrive. AI solutions come after them, with a label.