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 A006817 M3450 #28 May 12 2023 15:56:56 %S A006817 1,4,12,36,108,316,916,2628,7500,21268,60092,169092,474924,1329188, %T A006817 3715244,10359636,28856252,80220244,222847804,618083972,1713283628, %U A006817 4742946484,13123882524,36274940740,100226653420,276669062116,763482430316,2105208491748,5803285527724 %N A006817 Trails of length n on square lattice. %C A006817 A trail is a path which may cross itself but does not reuse an edge. This sequence counts directed paths on the square lattice. %D A006817 N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence). %H A006817 Andrey Zabolotskiy, <a href="/A006817/b006817.txt">Table of n, a(n) for n = 0..31</a> (from Conway & Guttmann; terms 0..30 from Bert Dobbelaere) %H A006817 A. R. Conway and A. J. Guttmann, <a href="https://doi.org/10.1088/0305-4470/26/7/013">Enumeration of self-avoiding trails on a square lattice using a transfer matrix technique</a>, J. Phys. A: Math. Gen., 26 (1993), 1535-1552; arXiv:<a href="https://arxiv.org/abs/hep-lat/9211063">hep-lat/9211063</a>, 1992. %H A006817 A. J. Guttmann, <a href="https://doi.org/10.1088/0305-4470/18/4/009">Lattice trails II: numerical results</a>, J. Phys. A 22 (1989), 575-588. %H A006817 A. Malakis, <a href="https://doi.org/10.1088/0305-4470/9/8/018">The trail problem on the square lattice</a>, J. Phys A 9 (8) (1976) p 1283. Table 1. %Y A006817 Undirected trails-rotation and reflection are counted by A001997. %Y A006817 Cf. A006818, A006819, A006851. %K A006817 nonn,walk %O A006817 0,2 %A A006817 _N. J. A. Sloane_ %E A006817 More terms from _David W. Wilson_, Jul 20 2001 %E A006817 More terms from _Bert Dobbelaere_, Jan 19 2019