%I
%S 1,2,5,13,36,98,272,740,2034,5513,15037,40617,110188,296806,802075,
%T 2155667,5808335,15582342,41889578,112212146,301100754,805570061,
%U 2158326727,5768299665,15435169364,41214098278,110164686454
%N Number of inequivalent selfavoiding walks of length n on a 2D lattice which start at origin, take first step in {+1,0} direction and if any steps are vertical, a step up is taken before a step down.
%H Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/SelfAvoidingWalk.html">SelfAvoiding Walk.</a>
%F a(n) = (A001411(n)+4)/8
%Y Cf. A046170.
%K nonn,walk,easy,nice
%O 1,2
%A _Eric W. Weisstein_
%E More terms from _Stephen A. Silver_
