Question 31
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 $n \in \mathbb{Z}$.
MathNet 2014 Question 31
Math Olympiad Vault · MathNet 2014