The maximum number of perfect matchings in graphs with a given degree sequence

We show that the number of perfect matching in a simple graph $G$ with an even number of vertices and degree sequence $d_1,d_2,\mathrm{.}\mathrm{.}\mathrm{.},d_n$ is at most ${\prod }_{i=1}^n(d_i!{)}^{\frac{1}{2d_i}}$. This bound is sharp if and only if $G$ is a union of complete balanced bipartite graphs.