1,3

An equivalent definition: Number of simple connected graphs with n nodes that have no subgraph isomorphic to the diamond graph or the complete graph K_4. This is the same because a graph contains a diamond as a subgraph iff it contains a diamond or K_4 as induced subgraph. - Falk Hüffner, Jan 11 2015

Travis Hoppe and Anna Petrone, Encyclopedia of Finite Graphs

Falk Hüffner, tinygraph, software for generating integer sequences based on graph properties, version ece94ef.

Eric Weisstein's World of Mathematics, Diamond Graph

Cf. A077269 (connected squarefree graphs).

Cf. also A242790 (diamond free graphs), A079574 (K_4 free graphs).

Sequence in context: A216810 A065851 A173938 * A013044 A110577 A335441

Adjacent sequences: A242787 A242788 A242789 * A242791 A242792 A242793

nonn,more

Travis Hoppe and Anna Petrone, May 22 2014

Entry revised by N. J. A. Sloane, Jan 11 2016

a(11) and a(12) added using tinygraph by Falk Hüffner, Jan 15 2016

approved