  Let $(P\in X,\Delta)$ be a three dimensional log canonical pair such that
$\Delta$ has only standard coefficients and $P$ is a center of log canonical
singularities for $(X,\Delta)$. Then we get an effective bound of the indices
of these pairs and actually determine all the possible indices. Furthermore,
under certain assumptions including the log Minimal Model Program, an effective
bound is also obtained in dimension $n\geq 4$.
