Extremal Graphs With a Given Number of Perfect Matchings

Abstract

Abstract Let denote the maximum number of edges in a graph having n vertices and exactly p perfect matchings. For fixed p , Dudek and Schmitt showed that for some constant when n is at least some constant . For , they also determined and . For fixed p , we show that the extremal graphs for all n are determined by those with vertices. As a corollary, a computer search determines and for . We also present lower bounds on proving that for (as conjectured by Dudek and Schmitt), and we conjecture an upper bound on . Our structural results are based on Lovász's Cathedral Theorem.