Question 3
Find all functions $f:\mathbb Z^+\to\mathbb Z^+$ satisfying
$$m!!+n!!\mid f(m)!!+f(n)!!$$
for each $m,n\in\mathbb Z^+$, where $n!!=(n!)!$ for all $n\in\mathbb Z^+$.
$$m!!+n!!\mid f(m)!!+f(n)!!$$
for each $m,n\in\mathbb Z^+$, where $n!!=(n!)!$ for all $n\in\mathbb Z^+$.