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 16 2022
REFERENCES
V. Jovovic, G. Kilibarda, Enumeration of labeled initially-finally connected digraphs, Scientific review, Serbian Scientific Society, 19-20 (1996), p. 244.
LINKS
Andrew Howroyd, Table of n, a(n) for n = 1..50
Sean A. Irvine, Java program (github)
V. Jovovic and G. Kilibarda, Enumeration of labeled quasi-initially connected digraphs, Discrete Math., 224 (2000), 151-163.
R. W. Robinson, Counting digraphs with restrictions on the strong components, Combinatorics and Graph Theory '95 (T.-H. Ku, ed.), World Scientific, Singapore (1995), 343-354.
PROG
(PARI) InitFinally(15) \\ See A057271. - Andrew Howroyd, Jan 16 2022
CROSSREFS
KEYWORD
nonn
AUTHOR
Vladeta Jovovic, Goran Kilibarda
EXTENSIONS
Terms a(12) and beyond from Andrew Howroyd, Jan 16 2022
STATUS
approved