

A133279


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


0



1, 0, 1, 1, 7, 21, 234, 2252, 64420, 2148355, 183956671
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OFFSET

1,5


COMMENTS

Mating graphs are graphs where no two nodes have the same set of neighbors.
Graphs with an invertible adjacency matrix are mating graphs.


LINKS

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


FORMULA

a(n) = A004110(n)  A109717(n).


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 && Length[Union[ToAdjacencyMatrix[lg[[ # ]]]]] == i &]]]]; k


CROSSREFS

Cf. A004110, A109717.
Sequence in context: A183938 A060146 A111878 * A192734 A220161 A213152
Adjacent sequences: A133276 A133277 A133278 * A133280 A133281 A133282


KEYWORD

nonn,more


AUTHOR

Tanya Khovanova, Aug 27 2008


EXTENSIONS

a(8)a(11) by Shreeyash Gotmare, Aug 28 2017


STATUS

approved



