$\newcommand{\xacomb}[2]{\raise{0.5em}{\small{#1}} C_{#2}}$ $\newcommand{\xaperm}[2]{\raise{0.5em}{\small{#1}} P_{#2}}$ $\newcommand{\xasuper}[1]{\raise{0.4em}{\underline{#1}}}$ $\newcommand{\xatooltipc}[2]{\xatooltip{\color{green}{#1}}{#2}}$ $\newcommand{\xatooltipcc}[3]{\xatooltip{\color{#1}{#2}}{#3}}$ $\newcommand{\xafactorial}[1]{\bbox[border-left: 1px solid black; border-bottom: 2px solid black; padding-left: 2px; padding-bottom: 2px; padding-right: 3px; padding-top: 2px;]{#1}}$ $\DeclareMathOperator{\sech}{sech}$ $\DeclareMathOperator{\csch}{csch}$