Question 6
Find all functions $f: \mathbb{Z} \rightarrow \mathbb{Z}$ such that
$$
n^{2}+4 f(n)=f(f(n))^{2}
$$
for all $n \in \mathbb{Z}$.
$$
n^{2}+4 f(n)=f(f(n))^{2}
$$
for all $n \in \mathbb{Z}$.
IMO 2014 — Complete Shortlist Question 6
IMO Shortlist · IMO 2014 — Complete Shortlist