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a(n) is the total area of all self-avoiding polygons of length 2n on the square lattice.
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%I #8 Apr 25 2022 22:35:20

%S 1,4,22,124,726,4352,26614,165204,1037672,6580424,42062040,270661328,

%T 1751614248,11391756176,74406502814,487838450116,3209229661682,

%U 21175301453040,140097533633112,929160187609096

%N a(n) is the total area of all self-avoiding polygons of length 2n on the square lattice.

%H I. Jensen, <a href="/A056625/b056625.txt">Table of n, a(n) for n = 2..43</a> (from link below)

%H I. Jensen, <a href="http://www.ms.unimelb.edu.au/~iwan/polygons/series/square.area_mom1.ser">More terms</a>

%Y Cf. A002931, A056631.

%K nonn

%O 2,2

%A _N. J. A. Sloane_, Aug 30 2000

%E Title clarified by _Sean A. Irvine_, Apr 25 2022