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Number of n X n symmetric binary matrices with each element either the sum mod 2 of its diagonal neighbors or the sum mod 2 of its antidiagonal neighbors
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%I #15 Dec 18 2015 18:17:12

%S 1,4,20,100,720,7920,156960,4978909,162844632,9658482053,917891979225,

%T 113051563311936,21440096665285608,6394092372716939840,

%U 2723634378368868283440,1747667851609071536512000

%N Number of n X n symmetric binary matrices with each element either the sum mod 2 of its diagonal neighbors or the sum mod 2 of its antidiagonal neighbors

%H R. H. Hardin, <a href="/A093440/b093440.txt">Table of n, a(n) for n = 1..21</a>

%e Some solutions for 5X5

%e ..0..0..1..1..0....0..0..1..0..0....1..1..1..1..1....0..0..1..1..1

%e ..0..0..0..1..1....0..1..0..1..0....1..1..1..1..0....0..0..1..1..1

%e ..1..0..1..0..1....1..0..1..1..1....1..1..0..0..0....1..1..0..1..0

%e ..1..1..0..1..0....0..1..1..0..1....1..1..0..0..1....1..1..1..0..0

%e ..0..1..1..0..0....0..0..1..1..0....1..0..0..1..0....1..1..0..0..0

%K nonn

%O 1,2

%A _R. H. Hardin_ Jun 26 2011