I apologise for a repost, but my rep is not high enough to ask in a comment. But, in this question Simplify sum of factorials with mathematical induction I am confused how:
$$(n+1)!-1+(n+1)(n+1)! = -1+(n+1)!(1+(n+1))$$
I expect it's quite simple, but I couldn't for the life of me see the solution. Any help would be much appreciated.