表格内的多行公式

\begin{tabular}{l c}
\hline
Phase NO. & S(k)\\
\hline
O$_{6c}$ &
\begin{minipage}{4in}
\begin{equation*}
\begin{aligned}
&\frac{4}{81}( 11 + 2\cos
(2k\pi ) +12\cos (4k\pi ) + 8\cos (6k\pi )+2\cos (8k\pi
)\\
&+10\cos(10k\pi)+4\cos(14k\pi)){\left(\sum_{n=0}^2
\cos(9k(2n+1)\pi)\right)}^2
\end{aligned}
\end{equation*}
\end{minipage}\\
\end{tabular}