Does anyone know the sum of all triangle numbers? I.e
1+3+6+10+15+21...
I've tried everything, but it might help you if I tell you one useful discovery I've made:
I know that the sum of alternating triangle numbers, 1-3+6-10... Is equal to 1/8 and that to change
1+3+6... Into 1-3+6... You would subtract 6+20+42+70... which is every other triangular number (not the hexagonals) multiplied by two.
1/8 plus this value is 1+3+6+10+...
A final note: I tried to split the triangle numbers into hexagonals and that series and then I got the squares of the odd numbers. Using dirichlet lambda functions This gave me 0 but I don't think this could be right. A number of other sums gave me -1/24 and 3/8 but I have no idea
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