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Is there a name for this series?

$\sum_{k=1}^{\infty}\frac{a^{2k}}{2k}.$

I know that:

$\tanh^{-1}(a)=\sum_{k=1}^{\infty}\frac{a^{2k-1}}{2k-1}.$

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    Yup I noticed. Was curious, if there is a name.2012-07-29

1 Answers 1

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I don't believe there's a name for the series you have there, but,

$\begin{align*} -\log(1-z)&=\sum_{k=1}^\infty\frac{z^k}{k}\\ -\log(1-z^2)&=\sum_{k=1}^\infty\frac{z^{2k}}{k}\\ -\frac12\log(1-z^2)&=\sum_{k=1}^\infty\frac{z^{2k}}{2k}\\ \log\frac1{\sqrt{1-z^2}}&=\sum_{k=1}^\infty\frac{z^{2k}}{2k}\\ \end{align*}$