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What is the sum of all the natural numbers ?

GROUPS:
There is a viral video, currently on the Net rounds,
alleging that "the sum of of all the natural numbers = - 1/12".

Anyone got a good "layman's suitable" debunk for this ?
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POSTED BY: Colin KLINE
Answer
6 months ago
It really depends on what is meant by the "sum of all the natural numbers". The series is divergent in the usual sense. Nevertheless, the statement is correct if understood in a regularization sense, i.e. looking at the analytic continuation of the Riemann zeta function to -1. Mathematica knows that
In[1]:= Zeta[-1]

Out[1]= -(1/12)

In[2]:= Sum[n^-s, {n, 1, Infinity}] /. s -> -1

Out[2]= -(1/12)
See this or this Wikipedia articles for more details.
POSTED BY: Ilian Gachevski
Answer
6 months ago
The videos (https://www.youtube.com/watch?v=w-I6XTVZXww and https://www.youtube.com/watch?v=E-d9mgo8FGk) somehow manage to avoid telling that this type of a sum has a name: it's Ramanujan summation (http://en.wikipedia.org/wiki/Ramanujan_summation).
POSTED BY: Jari Kirma
Answer
6 months ago