\begin{table}%T6
\caption{Close companions of RQQs and RLQs$^a$.}
\label{average}%\centerline
 {\small
\begin{tabular}{@{}lllll@{}}
\hline\hline
%\noalign{\smallskip}
Sample & $N_{\rm ave}$ & $N_{\rm ave}$ & $N_{\rm c}/N_{\rm tot}$ & $N_{\rm c}/N_{\rm tot}$ \\
 & (50~kpc) & (100~kpc) & (50~kpc) & (100~kpc) \\
%\noalign{\smallskip}
\hline
%\noalign{\smallskip}
RQQ & 0.27 $\pm$ 0.59 & 0.93 $\pm$ 1.03 & 20\% & 60\%\\
(this work) & & & & \\
FSRQ & 0.19 $\pm$ 0.39 & 1.19 $\pm$ 1.01 & 19\% & 75\%\\
(K98) & & & & \\
SSRQ & 0.05 $\pm$ 0.22 & 0.53 $\pm$ 0.68 & 5\%  & 42\%\\
(K00) & & & &\\
%\noalign{\smallskip}
\hline
\end{tabular}}
\medskip
\par
$^a$ Column (1) gives the sample; (2) the average number of companions within 50~kpc radius; 
(3) the average number of companions within 100~kpc radius; (4) and (5) the fraction of quasars 
with close companion within 50~kpc and 100~kpc radius, respectively.
\end{table}