Monday, 10 November 2014

sequences and series - Why does sum_{k=1}^infty (ζ[2k+1]-1)=frac{1}{4}




Can someone explain why



\sum_{k=1}^\infty (ζ[2k+1]-1)=\frac{1}{4}?


Answer



We can rearrange
\begin{align}\sum_{k=1}^\infty(\zeta(2k+1)-1)&=\sum_{k=1}^\infty\sum_{n=2}^\infty\frac1{n^{2k+1}}\\ &=\sum_{n=2}^\infty\sum_{k=1}^\infty\frac1{n^{2k+1}}\\ &=\sum_{n=2}^\infty\frac1{n(n^2-1)}\\ &=\sum_{n=2}^\infty\left(\frac1{2n(n-1)}-\frac1{2(n+1)n}\right)\\&=\frac14\end{align}



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