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 A307180 #9 May 12 2019 17:52:57 %S A307180 1,0,1,2,6,15,68,310,2096,16554,152497,1574652,17947667,223013311 %N A307180 Isomorphism classes of 2-in 2-out regular digraphs, allowing parallel edges but not loops. %H A307180 Richard J. Mathar, <a href="https://arxiv.org/abs/1903.12477">2-regular Digraphs of the Lovelock Lagrangian</a>, arXiv:1903.12477 [math.GM], 2019. %Y A307180 Cf. A306827 (connected, inverse Eul. Trans.) %K A307180 nonn,hard,more %O A307180 0,4 %A A307180 _R. J. Mathar_, Mar 28 2019