\documentclass[12pt]{article}
\usepackage{amssymb,amsmath,amscd,amstext,amsopn,amscd,amsfonts}
\pagestyle{empty}
\begin{document}
\begin{displaymath}
\label{e:barwq}\begin{split}
H_c&=\frac{1}{2n} \sum^n_{l=0}(-1)^{l}(n-{l})^{p-2}
\sum_{l _1+\dots+ l _p=l}\prod^p_{i=1} \binom{n_i}{l _i}\\
&\quad\cdot[(n-l )-(n_i-l _i)]^{n_i-l _i}\\
&\quad\cdot
\Bigl[(n-l )^2-\sum^p_{j=1}(n_i-l _i)^2\Bigr].
\end{split}
\end{displaymath}
\end{document}
