Question 139
Find all functions $f : \mathbb{Z}^+ \to \mathbb{Z}^+$ such that for each pair of positive integers $a$ and $b$,
$$
f(a) + 2ab + f(b)
$$
is a perfect square.
$$
f(a) + 2ab + f(b)
$$
is a perfect square.
MathNet 2019-part-03 — 184 problems (EN–VI) Question 139
Math Olympiad Vault · MathNet 2019-part-03 — 184 problems (EN–VI)