My favourite theorem is by the mysterious Indian mathematician Ramanujan. He came up with the following infinite series for pi:
- $ \frac{1}{\pi} = \frac{2\sqrt{2}}{9801} \sum^\infty_{k=0} \frac{(4k)!(1103+26390k)}{(k!)^4 396^{4k}}. $
Not only is it correct, but converges to pi very rapidly too. This is my favourite theorem because it seems so absurd!
