# Messing around with the abel-plana formula for $\sum_n \frac 1{n^3}$

I've just discovered the Abel-Plana formula: http://en.wikipedia.org/wiki/Argument_principle

I'm trying to use it to get a closed-form expression for $\sum_{n=1}^\infty \frac 1{n^3}$.

So far, I have the $$\sum_{n=1}^\infty \frac 1{n^3}= 1+2i\int_0^{\infty} \frac{dt}{\bigl(\exp(2\pi t)-1\bigr)(it+1)^3}.$$ This integral has poles at $t=0$ and $t=i$. I know I should use the residue theorem but I'm not sure how to apply it to this integral. Any thoughts would be appreciated.

PS- I know that the answer should be $\zeta(3)$ but I want to know what the Abel-Plana formula has to say about it.

• Thanks for Te(fi)xing that up for me :) I am studying for an exam right now and just thought of it on the fly.
– joe
Nov 16, 2012 at 7:53

## 1 Answer
