AMS Subject Classification: 05B05, 05E30, 05C50.

AMS classifications: 05E30, 05B20;

The energy of a graph is the sum of the absolute values of the eigenvalues of its adjacency matrix. Koolen and Moulton have proved that the energy of a graph on n vertices is at most n(1 + √n)/2, and that equality holds if and only if the graph is strongly regular with parameters (n,...