Question 28
Determine all natural numbers $n \ge 2$ for which
$$
n = a^2 + b^2
$$
holds, where $a$ is the smallest divisor of $n$ different from 1 and $b$ is an arbitrary divisor of $n$.
$$
n = a^2 + b^2
$$
holds, where $a$ is the smallest divisor of $n$ different from 1 and $b$ is an arbitrary divisor of $n$.