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A140636
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Number of connected graphs on n unlabeled nodes that contain at least two cycles.
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9
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0, 0, 0, 2, 13, 93, 809, 11005, 260793, 11715808, 1006698524, 164059824899, 50335907853919, 29003487462805642, 31397381142761123838, 63969560113225175845492, 245871831682084026518599099, 1787331725248899088890197955308, 24636021429399867655322650752269938
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OFFSET
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1,4
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COMMENTS
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Original name: number of unlabeled complex components with n nodes.
We can find in "The Birth of the Giant Component", p. 2, see the first link:
"As each of the random graphs evolved, the story went, never once was there more than a single 'complex' component; i.e. there never were two or more components present simultaneously that were neither trees nor unicyclic."
So a complex component is a connected graph that is neither a tree nor an unicyclic graph.
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LINKS
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FORMULA
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EXAMPLE
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a(4) = 2. See the two complex components with 4 nodes in the Sloane illustration.
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CROSSREFS
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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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