Value of Ramanujan Summation In Quantum Mechanics

Question

In mathematics, sum of all natural number is infinity.

but Ramanujan suggests whole new definition of summation.

"The sum of $n$ is $-1/12$" what so called Ramanujan Summation.

First he find the sum, only Hardy recognized the value of the summation.

And also in quantum mechanics(I know), Ramanujan summation is very important.

Question. What is the value of Ramanujan summation in quantum mechanics?

Answer 1

Lumo gives a very nice step by step calculation of this sum and a good discussion of the importance and application of such summation techniques in QFTs here:

http://motls.blogspot.com/2011/07/why-is-sum-of-integers-equal-to-112.html

Such mathematical calculations are NOT unrelated to physics; on the contrary they are important...