I need a little bit help with this:
Got to work my way from "sum from k=1 to n (k^2*n nCr k))" to this: (n^2+n)*2^(n-2), but HOW?
I´ve tried god-knows-what but nothing seems to work..
You can't prove that, it isn't true.
(Perhaps I am confused as to what "nCr" means. I thought that was the binomial coefficient but there is no "r" on the right, and it isn't an index so I assumed you meant "nCk".)