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%I #6 Dec 18 2015 18:17:40
%S 1,2,3,10,52,305,3336,53160,1210187,43234473,2296063392,180971357507,
%T 21523051916415,3822241812458992,1013512678870403979,
%U 402404564958432626790,238779216876700299752228
%N Number of n X n symmetric binary matrices with each element either the sum mod 2 of its horizontal neighbors or the sum mod 2 of its vertical neighbors
%H R. H. Hardin, <a href="/A192258/b192258.txt">Table of n, a(n) for n = 1..18</a>
%e Some solutions for 5X5
%e ..1..1..0..1..1....1..1..0..0..0....1..1..0..1..1....0..0..0..1..0
%e ..1..1..0..0..0....1..1..0..1..0....1..0..1..1..0....0..0..0..1..0
%e ..0..0..0..0..0....0..0..1..1..0....0..1..1..0..1....0..0..0..0..0
%e ..1..0..0..0..0....0..1..1..1..0....1..1..0..1..1....1..1..0..0..0
%e ..1..0..0..0..0....0..0..0..0..0....1..0..1..1..1....0..0..0..0..0
%K nonn
%O 1,2
%A _R. H. Hardin_ Jun 26 2011
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