What is the incorrect proof by Euler that $\pi = 0$ (or something like that)?

Question

I seem to remember a proof by Euler, involving infinite series, which was really complex (for a maths hobbyist). I believe it was sent in a letter to someone, and that it ended up with $\pi = 0$ or something. I was just wondering if anyone has any idea what I'm talking about, or if it was someone else.

Thanks.

Answer 1

$$e^{2i\pi}=1=e^0\quad=>\quad2i\pi=0\quad=>\quad\pi=\dfrac0{2i}=0.$$