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 A049531 Number of digraphs with a source and a sink on n unlabeled nodes. 9
 1, 2, 11, 173, 8675, 1483821, 870901739, 1786098545810, 13011539185371716, 341128981258340797839, 32519138088689298538132027, 11366354205366488038532562993809, 14668937734550708660348161757913398001, 70315451107713339843384354196009678853303102 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS 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 REFERENCES V. Jovovic, G. Kilibarda, Enumeration of labeled initially-finally connected digraphs, Scientific review, Serbian Scientific Society, 19-20 (1996), p. 246. LINKS Andrew Howroyd, Table of n, a(n) for n = 1..50 PROG (PARI) \\ See PARI link in A350794 for program code. A049531seq(15) \\ Andrew Howroyd, Jan 21 2022 CROSSREFS Row sums of A057278. The labeled version is A049524. Cf. A003085, A035512, A003088, A051421, A345258, A350794. Sequence in context: A121231 A122527 A039747 * A031508 A202140 A011806 Adjacent sequences: A049528 A049529 A049530 * A049532 A049533 A049534 KEYWORD nonn,nice AUTHOR Vladeta Jovovic, Goran Kilibarda EXTENSIONS a(6)-a(7) from Andrew Howroyd, Jan 01 2022 Terms a(8) and beyond from Andrew Howroyd, Jan 20 2022 STATUS approved

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Last modified December 9 19:36 EST 2022. Contains 358703 sequences. (Running on oeis4.)