%I #6 Jul 04 2018 20:26:38
%S 0,2,6,59,695,12198
%N Number of self-avoiding polygons with perimeter 2*n and sides = 1 that have vertex angles from the set 0, +-Pi/4, +-Pi/2, +-3*Pi/4, not counting rotations and reflections as distinct.
%C Holes are excluded, i.e., the boundary path may nowhere touch or intersect itself.
%H 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 Hugo Pfoertner, <a href="http://www.randomwalk.de/sequences/a316198.htm">Illustration of polygons of perimeter <= 10</a>.
%Y Cf. A306178, A316195, A316197.
%K nonn,walk,more
%O 1,2
%A _Hugo Pfoertner_, Jul 04 2018