\[\Large\sum_{n=1}^{\infty}\frac{\left(H_{n}^{(2)}\right)^{2}}{n^{2}}=\frac{19}{24}\zeta(6)+\zeta^{2}(3)\] \(\Large\mathbf{Proof:}\) We use the Abel's rearrangement over the \(N\)-th partial sum of the series, \[\begin{align*}\sum\limits_{n=1}^{N}\fr…
\[\Large\sum_{n=1}^{\infty} \frac{H_{n}}{2^nn^4}\] \(\Large\mathbf{Solution:}\) Let \[\mathcal{S}=\sum^\infty_{n=1}\frac{H_n}{n^42^n}\] We first consider a slightly different yet related sum. The main idea is to solve this sum with two different meth…