Extremal Triangle-Free Regular Graphs Containing A Cut Vertex

The exact values of \(c(n)\) are determined, where \(c(n)\) denotes the largest \(k\) for which there exists a triangle-free \(k\)-regular graph on \(n\) vertices containing a cut-vertex. As a corollary, we obtain a lower bound on the densest triangle-free regular graphs of given order that do not have a one-factorization.