Let $k$ and $m$ be positive integers. Show that \[S(m, k)=\sum_{n=1}^{\infty}\frac{1}{n(mn+k)}\] is rational if and only if $m$ divides $k$.
Problem
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Tags: rational numbers
25.05.2007 03:24
This problem is considered in russian forum
25.05.2007 03:24
Juna (or someone else), would you mind translating the solution for us?
25.05.2007 03:24
Actually, I don't think that this problem was solved in that topic,at least I didn't feel that it was after reading that topic . They are manly concerned with calculating the sum \[S(m;1)\] and I don't think that they are done even with that work :razz: .
25.05.2007 03:24
Peter wrote: Juna (or someone else), would you mind translating the solution for us? Try so Tiks wrote: Actually, I don't think that this problem was solved in that topic,at least I didn't feel that it was after reading that topic I did not speak that problem is solved completely. But is there proved that amount transcendental if $k|m$
09.01.2021 19:33
The question is equivalent to proving that the expression $\gamma +\psi(x)$ is irrational for $x\in\mathbb{Q}-\mathbb{N}$ where $\gamma$ is the euler-mascheroni constant and $\psi$ is the digamma function. Just refer a paper by M.Ram Murty and N. Saradha that proves that in this case they must in fact be transcendental. $\square$