I've got to reduce it to this
$n+1|n^3+3n^2+n+2$
$n+1|n^3+3n^2+1$
$n+1|2n^2+1$
$n+1|2n^2+2n-2n+1$
$n+1|2n(n+1)-2n+1$
$n+1|-2n+3-2$
$n+1|-2(n+1)+3$
$n+1|3$
All this using propertie $c|a \land c|b \implies c|a \pm b$, however, I don't know how to find the $n$ integers solutions.