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 A058337 #28 Feb 16 2025 08:32:43 %S A058337 1,1,1,3,12,90,2162,179098,51110788,48762860958,157117982629089, %T A058337 1735975636147643118,66687671220840028265672, %U A058337 9012793558387399546070260538,4328655012123103085159161399497333,7451986601800967792474321528025564017244,46329541711597124247394557123740768918978380463 %N A058337 Number of connected loop-free Eulerian digraphs with n nodes. %C A058337 Parallel edges are not allowed, but 2-cycles are allowed. Since these digraphs have an Eulerian circuit, being weakly-connected is the same as being strongly-connected. - _Brendan McKay_, Apr 04 2023 %D A058337 F. Harary and E. M. Palmer, Graphical Enumeration, Academic Press, NY, 1973, p. 219 (but there is an error). %D A058337 Ronald C. Read, email to _N. J. A. Sloane_, 28 August, 2000. %H A058337 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/EulerianGraph.html">Eulerian Graph</a> %F A058337 Inverse Euler transform of A058338. - _Andrew Howroyd_, Apr 12 2020 %Y A058337 Cf. A058338. %K A058337 nonn,nice,hard %O A058337 0,4 %A A058337 _N. J. A. Sloane_ %E A058337 a(7) (generated graphs with nauty, filtered and counted with Python) by _Pietro Battiston_, Feb 08 2014 %E A058337 a(8) and a(9) added and description clarified by _Brendan McKay_, May 05 2019 %E A058337 Terms a(10) and beyond from _Andrew Howroyd_, Apr 12 2020