[SOLVED] Sigma notation of a series. I have the formula 1+2+3+...+n = (n^2+n+1)/2, and I thinkthat this is the formula for the sum of a series. I need to write this thing in sigma notation, and then prove it by induction. I'm usually good and proving things by induction, but I can't even figure out how to get this thing into sigma notation! I think by pluging in values that this series is 3/2 + 2 + 3 + 4 + 5 + etc This seems like it should be easy, but wow I have been stumped for awhile. Help is appreciated.