Friday, 29 November 2013

integration - Elementary way to calculate the series sumlimitsinftyn=1fracHnn2n

I want to calculate the series of the Basel problem n=11n2 by applying the Euler series transformation. With some effort I got that




ζ(2)2=n=1Hnn2n.



I know that series like the n=1Hnn2n are evaluated here, but the evaluations end up with some values of the ζ function, like ζ(2),ζ(3).



First approach: Using the generating function of the harmonic numbers and integrating term by term, I concluded that



n=1Hnn2n=120ln(1x)x(x1)dx,



but I can't evaluate this integral with any real-analytic way.




First question: Do you have any hints or ideas to evaluate it with real-analytic methods?



Second approach: I used the fact that Hnn=nk=11k(n+k) and then, I changed the order of summation to obtain



n=1Hnn2n=k=12kk(m=2k1m2m).



To proceed I need to evaluate the



120x2k11xdx,




since m=2k1m2m=120x2k11xdx.



Second question: How can I calculate this integral?



Thanks in advance for your help.

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