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A133279 Number of unlabeled mating graphs with n nodes and a degenerate adjacency matrix. 0

%I

%S 1,0,1,1,7,21,234,2252,64420,2148355,183956671

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

%C Mating graphs are graphs where no two nodes have the same set of neighbors.

%C Graphs with an invertible adjacency matrix are mating graphs.

%F a(n) = A004110(n) - A109717(n).

%t 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

%Y Cf. A004110, A109717.

%K nonn,more

%O 1,5

%A _Tanya Khovanova_, Aug 27 2008

%E a(8)-a(11) by _Shreeyash Gotmare_, Aug 28 2017

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Last modified September 22 19:36 EDT 2021. Contains 347608 sequences. (Running on oeis4.)