How can I find a closed form formula for the following sum?
For $p\in\mathbb{Z}^+\land q\in\mathbb{Z}^+\setminus\{1\}$,
\begin{equation*}
\displaystyle\sum_{k=1}^\infty\dfrac{H_k^p}{k^q}
\end{equation*}
Only if $p\leqslant2$ and $q\leqslant2$, this sum is following:
\begin{equation*}
\displaystyle\sum_{k=1}^\infty\dfrac{H_k^p}{k^q}=\dfrac{(pq-q\delta_{p,1})^2+1}{p+q-q\delta_{p,1}}\zeta(p+q)
\end{equation*}
where $H_k$ is following
\begin{equation*}
H_k=\displaystyle\sum_{j=1}^{k}\dfrac{1}{j}
\end{equation*}
When $p=1$ and $q=2$,
\begin{equation*}
\displaystyle\sum_{k=1}^\infty\dfrac{H_k^1}{k^2}=2\zeta(3)
\end{equation*}
When $p=2$ and $q=2$,
\begin{equation*}
\displaystyle\sum_{k=1}^\infty\dfrac{H_k^2}{k^2}=\dfrac{17}{4}\zeta(4)
\end{equation*}
However, when ($p\geqslant3\land q\geqslant2$) or ($p\geqslant2\land p\geqslant3$), I've failed.
I think that my formula is wrong for all $p$ and $q$.
I've seen this answer.
Thank you.
p.s.
If $1\leqslant p\leqslant2$ and $2\leqslant q\leqslant4$,
\begin{align*}
\displaystyle\sum_{k=1}^\infty\dfrac{H_k^p}{k^q}=\dfrac{(pq-q\delta_{p,1})^2+1}{p+q-q\delta_{p,1}}\zeta(p+q)
-\sum _{k=1}^{q-2} \left(\frac{1}{4} (-1)^{q+1} \binom{q+1}{k} \zeta (k+p) \zeta (q-k)+\frac{\left((p q)^2+3\right) \zeta (p+q)}{2 (p+q)}\right)-\frac{1}{2} q \left(\sum _{k=1}^{p-2} \zeta (p-k) \zeta (k+q)\right)-\sum _{k=1}^{q-3} \frac{(p q+5) \zeta (k+p)^2}{q}
\end{align*}
when $p=2$ and $q=3$,
\begin{equation*}
\displaystyle\sum_{k=1}^\infty\dfrac{H_k^2}{k^3}=-\zeta(2)\zeta(3)+\dfrac{7}{2}\zeta(5)
\end{equation*}
when $p=2$ and $q=4$,
\begin{equation*}
\displaystyle\sum_{k=1}^\infty\dfrac{H_k^2}{k^4}=\dfrac{97\pi^6}{22680}-2\{\zeta(3)\}^2
\end{equation*}
MultipleZetaValuesfrom here: https://www.researchgate.net/publication/357601353_Mathematica_package_MultipleZetaValues .Example code:2 MultiZeta[{x, 1, 1}] + 2 MultiZeta[{x + 1, 1}] + MultiZeta[{x, 2}] + Zeta[x + 2] /. x -> 2 // MZExpand. gives: $\frac{17 \pi ^4}{360}$. – Mariusz Iwaniuk Jun 03 '25 at 09:07