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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
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
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.
Sequence in context: A121231 A122527 A039747 * A031508 A202140 A011806
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