%I M4304 #9 Mar 30 2012 18:36:10
%S 6,216,3706,44060,417486,3386912,24554562,163587572,1020918342,
%T 6050527496,34395992698,188971062108,1009130882494,5261414979024
%N Almost-convex polygons of perimeter 2n on square lattice.
%D I. G. Enting, A. J. Guttmann, L. B. Richmond and N. C. Wormald, Enumeration of almost-convex polygons on the square lattice, Random Structures Algorithms 3 (1992), 445-461.
%D N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
%K nonn
%O 8,1
%A _Simon Plouffe_