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%I #6 Dec 18 2015 18:17:40
%S 2,7,41,428,7588,235992,12750773,1196790145,195443817921,
%T 55484180929526,27388366928551712,23507551792998353446,
%U 35081808543792928475951,91032423727427789694636918,410722028606679785606473590135
%N Number of n X n symmetric binary matrices with each 1 adjacent to no more than 2 horizontally, vertically or diagonally neighboring 1s
%H R. H. Hardin, <a href="/A191601/b191601.txt">Table of n, a(n) for n = 1..17</a>
%e Some solutions for n=4
%e ..0..1..1..0....1..0..1..1....1..0..0..0....0..0..0..1....1..0..0..1
%e ..1..1..0..0....0..0..0..0....0..0..0..1....0..0..0..1....0..0..0..0
%e ..1..0..0..0....1..0..1..0....0..0..0..1....0..0..1..0....0..0..0..1
%e ..0..0..0..1....1..0..0..0....0..1..1..1....1..1..0..0....1..0..1..1
%K nonn
%O 1,1
%A _R. H. Hardin_ Jun 08 2011