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 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 (list; graph; refs; listen; history; text; internal format)
 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 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

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Last modified July 24 15:05 EDT 2021. Contains 346273 sequences. (Running on oeis4.)