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 A316199 #5 Jul 04 2018 20:26:46 %S A316199 0,0,8,17,472,7042 %N A316199 Number of self-avoiding polygons with perimeter 2*n and sides = 1 that have vertex angles from the set +-Pi/9, +-3*Pi/9, +-5*Pi/9, +-7*Pi/9, not counting rotations and reflections as distinct. %C A316199 Holes are excluded, i.e., the boundary path may nowhere touch or intersect itself. %H A316199 Contest Organizers, <a href="http://www.recmath.org/contest/Snakes/index.php">Al Zimmermann's Programming Contests - Snakes on a Plane</a>, Fall 2006. %H A316199 Hugo Pfoertner, <a href="http://www.randomwalk.de/sequences/a316199.htm">Illustration of polygons of perimeter <= 12</a>. %Y A316199 Cf. A306179, A316195, A316197, A316198. %K A316199 nonn,walk,more %O A316199 1,3 %A A316199 _Hugo Pfoertner_, Jul 04 2018