1 + 2 + 3 + 4 + 5.... = -1/12?

http://www.youtube.com/watch?v=w-I6XTVZXww
http://www.youtube.com/watch?v=E-d9mgo8FGk

https://en.wikipedia.org/wiki/Ramanujan_summation#Sum_of_divergent_series

The Numberphile videos imply that 1 + 2 + 3… = -1/12 but it seems that they’re not talking about the traditional sum.

They said something about it being useful in physics and I think string theory…

I think the sum is infinite or at least a non-negative number. I wonder why it is -1/12? I mean why not pi or something…
More:
https://en.wikipedia.org/wiki/1_%2B_2_%2B_3_%2B_4_%2B_⋯

See the other current thread (and the older thread).

Since there is an active thread on this, I’m closing this one.

Colibri
General Questions Moderator