A133206 Number of unlabeled graphs with n nodes and a degenerate adjacency matrix.

1, 1, 3, 7, 25, 99, 690, 6551, 133174, 4138641, 290045659

Offset: 1

Author

Tanya Khovanova, Aug 27 2008

Keywords

• more
• nonn

Comments

a(n) = A000088(n) - A109717(n)

Links

• Ali Sltan Ali AL-Tarimshawy, J. Siemons, Singular Graphs with Dihedral Group Action, arXiv:2006.12875 [math.CO], 2020.

Crossrefs

Cf. A000088, A109717.

Programs

Mathematica

k = {}; For[i = 1, i < 8, i++, lg = ListGraphs[i] ; len = Length[lg]; k = Append[k, Length[Select[Range[len], Det[ToAdjacencyMatrix[lg[[ # ]]]] == 0 &]]]]; k