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%I M5203 #8 Mar 30 2012 18:36:10
%S 28,1468,34680,535452,6302296,61400920,520788460,3976323744,
%T 27974148068,184411212644,1153389882896,6908837566500,39921952365008
%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 10,1
%A _Simon Plouffe_