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%I M1637 #29 Sep 23 2022 07:13:21
%S 1,2,6,19,63,216,756,2684,9638,34930,127560,468837,1732702,6434322,
%T 23993874,89805691,337237337,1270123530,4796310672,18155586993,
%U 68874803609,261803388854,996971935098,3802944302442,14528816598358
%N Number of fixed n-celled self-avoiding polygons on square lattice.
%C Translations, rotations and reflections are not allowed.
%D N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
%H I. Jensen, <a href="/A006724/b006724.txt">Table of n, a(n) for n = 1..42</a> (from link below)
%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. See p. 477.
%H I. Jensen, <a href="https://web.archive.org/web/20160102114247/http://www.ms.unimelb.edu.au/~iwan/polygons/series/square.area.ser">More terms</a>
%H Tomás Oliveira e Silva, <a href="http://sweet.ua.pt/tos/animals.html">Enumeration of polyominoes</a>
%Y Cf. A002931.
%K nonn,nice
%O 1,2
%A _N. J. A. Sloane_, _Simon Plouffe_
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