This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A049531 #19 Jan 22 2022 23:42:12 %S A049531 1,2,11,173,8675,1483821,870901739,1786098545810,13011539185371716, %T A049531 341128981258340797839,32519138088689298538132027, %U A049531 11366354205366488038532562993809,14668937734550708660348161757913398001,70315451107713339843384354196009678853303102 %N A049531 Number of digraphs with a source and a sink on n unlabeled nodes. %C A049531 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 A049531 V. Jovovic, G. Kilibarda, Enumeration of labeled initially-finally connected digraphs, Scientific review, Serbian Scientific Society, 19-20 (1996), p. 246. %H A049531 Andrew Howroyd, <a href="/A049531/b049531.txt">Table of n, a(n) for n = 1..50</a> %o A049531 (PARI) \\ See PARI link in A350794 for program code. %o A049531 A049531seq(15) \\ _Andrew Howroyd_, Jan 21 2022 %Y A049531 Row sums of A057278. %Y A049531 The labeled version is A049524. %Y A049531 Cf. A003085, A035512, A003088, A051421, A345258, A350794. %K A049531 nonn,nice %O A049531 1,2 %A A049531 _Vladeta Jovovic_, Goran Kilibarda %E A049531 a(6)-a(7) from _Andrew Howroyd_, Jan 01 2022 %E A049531 Terms a(8) and beyond from _Andrew Howroyd_, Jan 20 2022