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 A055974 #8 Apr 19 2020 18:24:01 %S A055974 0,1,4,52,1504,145984,48461696,56141454464,229148544420864, %T A055974 3333310786076963968,174695272746603272722432, %U A055974 33301710992539090379269318144,23278728241293494481773139193036800,60084295633556503802059558812644803074048,576025077880237078776946485247979728479746359296 %N A055974 Number of unlabeled digraphs with loops (relations) on n nodes and with an odd number of arcs. %H A055974 Andrew Howroyd, <a href="/A055974/b055974.txt">Table of n, a(n) for n = 0..50</a> %F A055974 a(2*n) = (A000595(2*n) - A047832(n))/2; a(2*n+1) = A000595(2*n+1)/2. %F A055974 a(n) = (A000595(n) - A000171(2*n+1))/2. %Y A055974 Cf. A000171, A000595, A047832, A054960, A055973. %K A055974 easy,nonn %O A055974 0,3 %A A055974 _Vladeta Jovovic_, Jul 19 2000 %E A055974 a(0)=0 prepended and terms a(13) and beyond from _Andrew Howroyd_, Apr 19 2020