All Primitive Strongly Regular Graphs Except Four Are Hyperenergetic

The energy of a graph G, denoted by E(G), is the sum of the absolute values of the eigenvalues of G. If G is a graph on n vertices and E(G)\u3e2(n-1), then G is called a hyperenergetic graph. In this paper, we prove that all primitive strongly regular graphs except srg(5,2,0,1), srg(9,4,1,2), srg(10,3,0,1), and srg(16,5,0,2) are hyperenergetic. © 2011 Elsevier Ltd. All rights reserved