can someone find $\displaystyle \sum-{i=1}^{\infty}1\frac{i}$??
thanks
That's a very well-known problem with the nice answer $\displaystyle \frac{\pi^2}{6}$ but it's not trivial to find this result.
This pdf file contains 14 (!) different proofs for it, some a bit more understandable than others, depending on your mathematical background.