%I #10 Jul 03 2018 04:17:58
%S 1,6,33,306,2765,26290
%N Number of unrooted self-avoiding walks with n steps that can make turns from the set 0, +-Pi/6, +-2*Pi/6, +-3*Pi/6, +-4*Pi/6, +-5*Pi/6.
%C The turning angles are those of the regular 12-gon, with one vertex corresponding to the forbidden U-turn. The path may neither intersect nor touch itself anywhere.
%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/a306182.htm">Illustration of walks of lengths <= 3</a>.
%Y Cf. A266925, A037245, A306175, A151541, A306177, A306178, A306179, A306180, A306181.
%K nonn,walk,more
%O 1,2
%A _Hugo Pfoertner_, Jun 23 2018