By convention, empty graphs are considered edge-transitive.
Table of n, a(n) for n=1..10.
Eric Weisstein's World of Mathematics, Symmetric Graph
Cf. A133181 (number of connected symmetric graphs on n nodes).
Cf. A087145 (number of disconnected symmetric graphs on n nodes).
Sequence in context: A101200 A122585 A057449 * A265701 A007439 A238622
Adjacent sequences: A286928 A286929 A286930 * A286932 A286933 A286934
Eric W. Weisstein, May 16 2017