I have the following code

\begin{flushleft}

\begin{tabular}{ |c|c|c c| }

\hline

0 & 2 & 8 & 10 \\

1 & 3 & 9 & 11 \\

\cline{1-2}

4 & 6 & 12 & 14 \\

5 & 7 & 13 & 15 \\

\hline

16 & 18 & 24 & 26 \\

17 & 19 & 25 & 27 \\

20 & 22 & 28 & 30 \\

21 & 23 & 29 & 31 \\

\hline

\end{tabular}

\tab has $2^5$ elements

\end{flushleft}

The vertical lines extend the entire length of the table but I only need the vertical lines to extend halfway down the table. How can I do this?