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%I #16 Jan 08 2019 19:08:57
%S 0,1,1,3,4,16,23,87
%N Number of symmetric self-avoiding polygons on square lattice with perimeter 2*n, not counting rotations and reflections as distinct.
%C The sequence includes polygons of 2-fold, i.e., mirror or rotational, and higher (order >= 4) symmetry.
%H Hugo Pfoertner, <a href="http://www.randomwalk.de/sequences/a316194.htm">Illustration of polygons of perimeter <= 16</a>.
%Y Cf. A002931, A266549, A316196, A323188, A323189.
%K nonn,walk,more
%O 1,4
%A _Hugo Pfoertner_, Jun 27 2018
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