If you look at the second comment on this question here: http://physics.stackexchange.com/q/5207/34235 http://physics.stackexchange.com/q/5207/34235 it touches

If you look at the second comment on this question here: http://physics.stackexchange.com/q/5207/34235 http://physics.stackexchange.com/q/5207/34235 it touches on the explanation as to why bosonic string theory has 26 dimensions (as a result of this sum of natural numbers resulting in -1/12)