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Search: id:A139625
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| A139625 |
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Table read by rows: T(n,k) is the number of strongly connected directed multigraphs with loops and no vertex of degree 0, with n arcs and k vertices, which are transitive (the existence of a path between two points implies the existence of an arc between those two points). |
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5
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| 1, 1, 1, 1, 1, 1, 2, 1, 6, 1, 10, 1, 19, 1, 28, 1, 1, 44, 2, 1, 60, 10, 1, 85, 31, 1, 110, 90, 1, 146, 222, 1, 182, 520, 1, 231, 1090, 1, 1, 280, 2180, 2, 1, 344, 4090, 11, 1
(list; graph; listen)
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OFFSET
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1,7
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COMMENT
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Length of the n^th row: floor(sqrt(n)).
These graphs are reflexive (each vertex has a self-loop), so T(n,k) = sum(A139621(n-k^2,m),m=0..k)
T(n,1) = 1, T(n,2) = A005993(n-4), T(n,3) = A050927(n-9), T(n,4) = A050929(n-16).
Row sums: A139630.
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CROSSREFS
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Cf. A139623, A139624.
Sequence in context: A166120 A007956 A107754 this_sequence A053785 A060173 A059344
Adjacent sequences: A139622 A139623 A139624 this_sequence A139626 A139627 A139628
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KEYWORD
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nonn
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AUTHOR
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Benoit Jubin (benoit_jubin(AT)yahoo.fr), May 01 2008, Sep 01 2008
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