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%I M4523 #15 Jul 07 2015 17:42:48
%S 1,8,40,168,676,2672,10376,39824,151878,576656,2181496,8229160,
%T 30974700,116385088,436678520,1636472360,6126647748
%N Number of n-celled polygons with perimeter 2n 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 4,2
%A _N. J. A. Sloane_, _Simon Plouffe_