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%I #19 Jan 22 2022 23:42:12
%S 1,2,11,173,8675,1483821,870901739,1786098545810,13011539185371716,
%T 341128981258340797839,32519138088689298538132027,
%U 11366354205366488038532562993809,14668937734550708660348161757913398001,70315451107713339843384354196009678853303102
%N Number of digraphs with a source and a sink on n unlabeled nodes.
%C 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
%D V. Jovovic, G. Kilibarda, Enumeration of labeled initially-finally connected digraphs, Scientific review, Serbian Scientific Society, 19-20 (1996), p. 246.
%H Andrew Howroyd, <a href="/A049531/b049531.txt">Table of n, a(n) for n = 1..50</a>
%o (PARI) \\ See PARI link in A350794 for program code.
%o A049531seq(15) \\ _Andrew Howroyd_, Jan 21 2022
%Y Row sums of A057278.
%Y The labeled version is A049524.
%Y Cf. A003085, A035512, A003088, A051421, A345258, A350794.
%K nonn,nice
%O 1,2
%A _Vladeta Jovovic_, Goran Kilibarda
%E a(6)-a(7) from _Andrew Howroyd_, Jan 01 2022
%E Terms a(8) and beyond from _Andrew Howroyd_, Jan 20 2022