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Strongly Regular Graphs Admitting an Automorphism Group with Two Orbits

Nick C.Fiala1
1 Department of Mathematics St. Cloud State University St. Cloud, MN 56301

Abstract

In this note, motivated by the non-existence of a vertex-transitive strongly regular graph with parameters (3250,57,0,1), we obtain a feasibility condition concerning strongly regular graphs admitting an automorphism group with exactly two orbits on vertices. We also establish a result on the possible orbit sizes of a potential strongly regular graph with parameters (3250,57,0,1). We use our results to obtain a list of only 11 possible orbit size combinations for a potential strongly regular graph with parameters (3250,57,0,1) admitting an automorphism group with exactly two orbits.