MJaxEq

$

 \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}\genfrac{\left)}{\right)}{}{0pt}{1}{2} \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