Hi! I’m stuck with evaluating the following sum:
Sum[Tanh[(Pi*i/2)/i^5], {i, 1, Infinity}]
I thought of solving it using the Riemann Zeta functions but didn’t quite get it and and wolfram provides only a numerical value. How would you go about solving it step by step? Thank you!
I couln’t go beyond this
Map[Sum[#, {i, 1, Infinity}] &,
Tanh[Pi*i/2]/i^5 // TrigToExp // Apart]
I think that does not have finite closed-form expression in terms of very large class of special functions.
\sum _{i=1}^{\infty } \frac{\tanh \left(\frac{i \pi }{2}\right)}{i^5}=\\\zeta (5)-2 \sum _{k=1}^{\infty } \text{Li}_5\left(e^{-k \pi }\right)+4
\sum _{k=1}^{\infty } \text{Li}_5\left(e^{-2 k \pi }\right)=\\\zeta (5)-2* \text{A255701}+4* \text{A255702}
Where A255701 and A255702
{NSum[Tanh[(i \[Pi])/2]/i^5, {i, 1, Infinity},
WorkingPrecision -> 31],
Zeta[5] -
N[Sum[2 PolyLog[5, E^(-k \[Pi])] - 4 PolyLog[5, E^(-2 k \[Pi])], {k,
1, 1000}], 21]}
(*{0.9539629221432281032692, 0.9539629221432281032692}*)
Regards M.I.