Question 443419
Rewrite (n+1)! as  (n+1) * n * (n-1) * (n-2)! 

{{{((n+1) * n * (n-1) * (n-2)!)/(3!(n-2)!)}}}
{{{((n+1) * n * (n-1) * cross((n-2)!))/(3!cross((n-2)!))}}}
{{{((n^2+n)(n-1)) / (3*2*1)}}}
{{{highlight((n^3 - n) / 6)}}}