It may be better to look at a series in general: http://en.wikipedia.org/wiki/Convergent_series http://en.wikipedia.org/wiki/Convergent_series http://en.wikip

It may be better to look at a series in general: http://en.wikipedia.org/wiki/Convergent_series http://en.wikipedia.org/wiki/Convergent_series http://en.wikipedia.org/wiki/Divergent_series http://en.wikipedia.org/wiki/Divergent_series In particular there are many interesting sums on the convergent series page.