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

1,3

Comments

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

Links

Table of n, a(n) for n=1..11.

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

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

Crossrefs

Cf. A000088, A109717.

Sequence in context: A120540 A176829 A352385 * A054092 A096648 A156100

Adjacent sequences: A133203 A133204 A133205 * A133207 A133208 A133209

Keyword

more,nonn

Author

Tanya Khovanova, Aug 27 2008

Status

approved