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Search: id:A133279
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| A133279 |
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Number of unlabeled mating graphs with n nodes and a degenerate adjacency matrix. |
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+0
1
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OFFSET
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1,5
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COMMENT
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Mating graphs are graphs where no two nodes have the same set of neighbors.
Graphs with an invertible adjacency matrix are mating graphs.
a(n) = A004110(n) - A109717(n).
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MATHEMATICA
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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
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CROSSREFS
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Cf. A004110, A109717.
Sequence in context: A084711 A060146 A111878 this_sequence A082826 A130740 A101119
Adjacent sequences: A133276 A133277 A133278 this_sequence A133280 A133281 A133282
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KEYWORD
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more,nonn
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AUTHOR
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Tanya Khovanova (tanyakh(AT)yahoo.com), Aug 27 2008
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