There are four strongly regular graphs with parameters (ν, k, λ, μ) = (28, 12, 6, 4), one of them being the triangular graph of order 8. The other three such graphs are known as the Chang graphs, illustrated above. The Chang graphs are also cospectral with the triangular graph T_8, all having graph spectrum (-2)^20 4^7 12^1, meaning none of the these is determined by spectrum. The Chang graphs are distance-regular with intersection array {12, 5;1, 4} but are not distance-transitive. They are pancyclic. The Chang graphs are implemented in the Wolfram Language as GraphData[{Chang, n}] for n = 1, 2, 3.

determined by spectrum | Paulus graphs | strongly regular graph | triangular graph