%I M1623 #16 Mar 31 2012 10:23:10
%S 1,2,6,18,55,174,566,1868,6237,21050,71666,245696,847317,2937116,
%T 10226574,35746292,125380257,441125966,1556301578,18155586993
%N Number of n-celled polygons with perimeter 2n+2 on square lattice.
%D N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
%H I. G. Enting and A. J. Guttmann, <a href="http://dx.doi.org/10.1007/BF01112757">On the area of square lattice polygons</a>, J. Statist. Phys., 58 (1990), 475-484.
%K nonn
%O 1,2
%A _N. J. A. Sloane_, _Simon Plouffe_
%E Title corrected by _David Bevan_, Sep 28 2011