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 A006818 M4203 #23 Jul 08 2025 16:56:06 %S A006818 1,6,30,150,738,3570,17118,81498,385710,1817046,8528478,39903462, %T A006818 186198642,866861394,4027766490,18681900270,86518735722,400136695074, %U A006818 1848320799438,8528448008214 %N A006818 Trails of length n on hexagonal lattice. %C A006818 The hexagonal lattice is the familiar 2-dimensional lattice in which each point has 6 neighbors. This is sometimes called the triangular lattice. %D A006818 N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence). %H A006818 A. J. Guttmann, <a href="http://dx.doi.org/10.1088/0305-4470/18/4/009">Lattice trails II: numerical results</a>, J. Phys. A 22 (1989), 575-588. %H A006818 G. Nebe and N. J. A. Sloane, <a href="http://www.math.rwth-aachen.de/~Gabriele.Nebe/LATTICES/A2.html">Home page for hexagonal (or triangular) lattice A2</a> %K A006818 nonn,walk,more %O A006818 0,2 %A A006818 _N. J. A. Sloane_ %E A006818 a(17)-a(19) from _Sean A. Irvine_, Aug 15 2020