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 A219894 #12 Mar 12 2019 07:24:53 %S A219894 1,4,9,55,453,4357,47598,569769,7371560,102525991,1525164223 %N A219894 Number of directed 2-regular graphs on n nodes without directed 2-cycles. %H A219894 Gunnar Brinkmann, <a href="https://doi.org/10.1016/j.disc.2012.09.014">Generating regular directed graphs</a>, Discrete Math., 313 (2012), 1-7. %Y A219894 Cf. A096368, A219889, A219890, A219891, A219892, A219893, A219895. %K A219894 nonn,more %O A219894 5,2 %A A219894 _N. J. A. Sloane_, Nov 30 2012 %E A219894 a(14) and a(15) from _Brendan McKay_, Mar 12 2019