IMO Shortlist 2004 problem N3


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April 2, 2012
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Find all functions f: \mathbb{N^{*}}\to \mathbb{N^{*}} satisfying
\left(f^{2}\left(m\right)+f\left(n\right)\right) \mid \left(m^{2}+n\right)^{2}
for any two positive integers m and n.

Remark. The abbreviation \mathbb{N^{*}} stands for the set of all positive integers:
\mathbb{N^{*}}=\left\{1,2,3,...\right\}.
By f^{2}\left(m\right), we mean \left(f\left(m\right)\right)^{2} (and not f\left(f\left(m\right)\right)).
Source: Međunarodna matematička olimpijada, shortlist 2004