olymmath

ISL 2020 A6

  • Answer

Determine all functions f:Z→Zf: \mathbb{Z} \rightarrow \mathbb{Z} such that fa2+b2(a+b)=af(a)+bf(b) for every a,b∈Zf^{a^{2}+b^{2}}(a+b)=a f(a)+b f(b) \text { for every } a, b \in \mathbb{Z} Here, fnf^{n} denotes the nth n^{\text {th }} iteration of ff, i.e., f0(x)=xf^{0}(x)=x and fn+1(x)=f(fn(x))f^{n+1}(x)=f\left(f^{n}(x)\right) for all n⩾0n \geqslant 0.

Dataset text NuminaMath olympiads. Quoted with source.

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f(x) = x + 1 \text{ or } f(x) \equiv 0

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