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 A308239 #11 Apr 10 2020 21:05:33 %S A308239 1,1,0,1,1,4,16,175,5274,434017,90658149,48825116761,68579602126387, %T A308239 254236892409251687,2512196983110257299898,66738846701458593981832314, %U A308239 4802164152196181961357340585741,942009012794429918939576183310877477,506665422212653541096106256584713063500057 %N A308239 Number of isomorphism classes of connected Eulerian oriented graphs with n vertices. %C A308239 Loops and 2-cycles are not permitted. Eulerian means that each vertex has equal in-degree and out-degree. %F A308239 Inverse Euler transform of A308161. %Y A308239 Cf. A308161. %K A308239 nonn,hard %O A308239 0,6 %A A308239 _Alois P. Heinz_, May 16 2019 %E A308239 Terms a(12) and beyond from _Andrew Howroyd_, Apr 10 2020