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 A054956 #18 Aug 27 2019 10:11:49
%S A054956 0,0,2,64,3808,687616,438948304,1023160166400,8829110850999296,
%T A054956 284886609918480818176,34640035331694391925165824,
%U A054956 15970703846423879100651622752256,28060860469435555251136195646902620160,188681219498365676664628141013181314824798208
%N A054956 Number of labeled Eulerian digraphs with n nodes and an odd number of edges.
%H A054956 V. A. Liskovets, <a href="http://www.cs.uwaterloo.ca/journals/JIS/VOL3/LISK/Derseq.html">Some easily derivable sequences</a>, J. Integer Sequences, 3 (2000), #00.2.2.
%F A054956 a(n) = (A007080(n) - n!)/2. - _Andrew Howroyd_, Sep 10 2018
%t A054956 A007080 = Cases[Import["https://oeis.org/A007080/b007080.txt", "Table"], {_, _}][[All, 2]];
%t A054956 a[n_] := (A007080[[n]] - n!)/2;
%t A054956 Array[a, 14] (* _Jean-François Alcover_, Aug 27 2019 *)
%Y A054956 Cf. A007080, A054955.
%K A054956 nonn,easy
%O A054956 1,3
%A A054956 _N. J. A. Sloane_, May 24 2000
%E A054956 More terms from _Vladeta Jovovic_, Mar 05 2001
%E A054956 a(12)-a(14) from _Andrew Howroyd_, Sep 10 2018