

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
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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 initiallyfinally connected.  Andrew Howroyd, Jan 01 2022


REFERENCES

V. Jovovic, G. Kilibarda, Enumeration of labeled initiallyfinally connected digraphs, Scientific review, Serbian Scientific Society, 1920 (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



