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A368835
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Number of unlabeled n-edge loop-graphs with at most n vertices such that it is not possible to choose a different vertex from each edge.
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15
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0, 0, 0, 1, 5, 23, 98, 394, 1560, 6181, 24655, 99701, 410513, 1725725, 7423757, 32729320, 148027044, 687188969, 3275077017, 16022239940, 80431483586, 414094461610, 2185052929580, 11808696690600, 65312048149993, 369408792148714, 2135111662435080, 12601466371445619
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OFFSET
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0,5
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LINKS
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FORMULA
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EXAMPLE
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Non-isomorphic representatives of the a(4) = 5 loop-graphs:
{{1,1},{2,2},{3,3},{1,2}}
{{1,1},{2,2},{1,2},{1,3}}
{{1,1},{2,2},{1,2},{3,4}}
{{1,1},{2,2},{1,3},{2,3}}
{{1,1},{1,2},{1,3},{2,3}}
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MATHEMATICA
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Table[Length[Union[sysnorm /@ Select[Subsets[Subsets[Range[n], {1, 2}], {n}], Select[Tuples[#], UnsameQ@@#&]=={}&]]], {n, 0, 5}]
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CROSSREFS
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Without the choice condition we have A368598.
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KEYWORD
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nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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