Ramanujan's claim [duplicate]

I was reading about the mathematician Ramanujan, and he claimed that 1+2+3+4+5+...=-1/12, and that this is related to the Riemann Zeta Function. Can someone explain the relationship? (By the way, I don't know much about the Riemann Zeta Function, other that its related to primes) Thanks in advance!

• @JavaMan: Most of the answers to the questions you linked only deal with geometric series like $1+2+4+8+\cdots=-1$. – Rahul Feb 13 '13 at 6:17
• @Rn: You are correct. I will remove my comment as the exact duplicate has been found anyways. – JavaMan Feb 13 '13 at 22:01