$
\newcommand{\Re}{\mathrm{Re}\,}
\newcommand{\pFq}[5]{{}_{#1}\mathrm{F}_{#2} \left( \genfrac{}{}{0pt}{}{#3}{#4} \bigg| {#5} \right)}
$ [math] \begin{align} W_n (s) &:= \int_{[0, 1]^n} \left| \sum_{k = 1}^n \mathrm{e}^{2 \pi \mathrm{i} \, x_k} \right|^s \mathrm{d}\boldsymbol{x} \end{align} [/math] [math] \begin{align} W_3(k) &= \mathrm{Re} \, {}_{3}\mathrm{F}_{2}\left( \genfrac{}{}{0pt}{\frac{1}{2},-\frac{k}{2},-\frac{k}{2}}{\Pi} \right) \end{align} [/math]
\pFq32{\frac12, -\frac k2, -\frac k2}{1, 1}{4}.
W_3(k) &= \mathrm{Re} \, {}_{3}\mathrm{F}_{2}\left(\genfrac{}{}{0pt}{\frac{1}{2},-\frac{k}{2},-\frac{k}{2}}{\Pi}\right
