if $n^2+1$ is composite, then $n!+n^2+1$ is composite

Question

Prove if $n^2+1$ is composite, then $n!+n^2+1$ is composite I try to let $n^2+1$ = ad for some a,d $\in$ Z, but I find it doesn't work Just want to know the main idea for this problem

Answer 1

Hint If $n^2+1=ad$ show that $a \leq n$ or $d \leq n$.