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A049531
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Number of digraphs with a source and a sink on n unlabeled nodes.
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9
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1, 2, 11, 173, 8675, 1483821, 870901739, 1786098545810, 13011539185371716, 341128981258340797839, 32519138088689298538132027, 11366354205366488038532562993809, 14668937734550708660348161757913398001, 70315451107713339843384354196009678853303102
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OFFSET
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1,2
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COMMENTS
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Here a source is defined to be a node which has a directed path to all other nodes and a sink to be a node to which all other nodes have a directed path. A digraph with a source and a sink can also be described as initially-finally connected. - Andrew Howroyd, Jan 01 2022
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REFERENCES
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V. Jovovic, G. Kilibarda, Enumeration of labeled initially-finally connected digraphs, Scientific review, Serbian Scientific Society, 19-20 (1996), p. 246.
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LINKS
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PROG
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(PARI) \\ See PARI link in A350794 for program code.
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CROSSREFS
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KEYWORD
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nonn,nice
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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