\begin{equation*}A_{n} 		\equiv 		\begin{cases} 			0 & (\textrm{for}\ n\ \textrm{is odd}) \\ 			\left(\frac{(n-1)!!}{n!!}\right)^2 & (\textrm{for}\ n\ \textrm{is even}) 		\end{cases} 	\end{equation*}
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