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A308111
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Isomorphism classes of Eulerian digraphs with n vertices, allowing loops.
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5
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1, 2, 6, 24, 160, 2512, 129816, 22665792, 13056562208, 24953006054144, 160860329639968800, 3555065836569542246400, 273147301191314006316868352, 73832333258502021627712839197696, 70920540648597652305602460997787710080, 244186544390677638132290202415190606165938176, 3036252267734950687777830287721323374283100639476736
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OFFSET
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0,2
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COMMENTS
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Eulerian means that for every vertex the in-degree equals the out-degree.
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LINKS
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FORMULA
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EXAMPLE
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For n=2 the a(2)=6 solutions are: two non-adjacent vertices with or without loops (3 cases), two vertices with or without loops connected by edges in each direction (3 cases).
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CROSSREFS
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For labeled digraphs rather than isomorphism classes see A229865.
For isomorphism classes with loops forbidden see A058338.
Cf. A308128 (connected version of this).
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KEYWORD
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nonn,hard
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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