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 A003028 M3157 #35 Apr 14 2023 10:52:39 %S A003028 1,3,51,3614,991930,1051469032,4366988803688,71895397383029040, %T A003028 4719082081411731363408,1237678715644664931691596416, %U A003028 1297992266840866792981316221144960,5444416466164313011147841248189209354496,91343356480627224177654291875698256656613808896 %N A003028 Number of digraphs on n labeled nodes with a source. %C A003028 Here a source is a node that is connected by a directed path to every other node in the digraph (but does not necessarily have indegree zero). - _Geoffrey Critzer_, Apr 14 2023 %D A003028 V. Jovovic and G. Kilibarda, Enumeration of labeled initially-finally connected digraphs, Scientific review, Serbian Scientific Society, 19-20 (1996) 237-247. %D A003028 R. W. Robinson, Counting labeled acyclic digraphs, pp. 239-273 of F. Harary, editor, New Directions in the Theory of Graphs. Academic Press, NY, 1973. %D A003028 N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence). %H A003028 Andrew Howroyd, <a href="/A003028/b003028.txt">Table of n, a(n) for n = 1..50</a> %H A003028 V. Jovovic and G. Kilibarda, <a href="http://dx.doi.org/10.1016/S0012-365X(00)00112-6">Enumeration of labeled quasi-initially connected digraphs</a>, Discrete Math., 224 (2000), 151-163. %o A003028 (PARI) Initially(12) \\ See A057274. - _Andrew Howroyd_, Jan 11 2022 %Y A003028 The unlabeled version is A051421. %Y A003028 Row sums of A057274. %Y A003028 Column k=1 of A361579. %Y A003028 Cf. A003027, A003029, A003030, A049524, A049414, A350792. %K A003028 nonn,easy,nice %O A003028 1,2 %A A003028 _N. J. A. Sloane_ %E A003028 Corrected and extended by _Vladeta Jovovic_, Goran Kilibarda %E A003028 Terms a(12) and beyond from _Andrew Howroyd_, Jan 11 2022