%I
%S 1,2,4,24,224,2862,53010,1527552,65195940,4097065492,385902826186,
%T 54089022594864,11269850153217786,3491854976674289164,
%U 1609153719436211880868,1102542409006001885651456
%N Half the number of n X n symmetric binary matrices with no element unequal to a strict majority of its diagonal and antidiagonal neighbors
%H R. H. Hardin, <a href="/A190655/b190655.txt">Table of n, a(n) for n = 1..18</a>
%e Some solutions for n=5 with a(1,1)=0
%e ..0..1..1..0..1....0..1..0..0..1....0..1..0..1..1....0..1..0..0..1
%e ..1..0..0..1..1....1..0..1..1..0....1..0..1..1..0....1..0..1..1..0
%e ..1..0..0..1..0....0..1..1..0..0....0..1..1..0..0....0..1..0..0..1
%e ..0..1..1..0..0....0..1..0..0..1....1..1..0..0..1....0..1..0..0..0
%e ..1..1..0..0..0....1..0..0..1..0....1..0..0..1..0....1..0..1..0..0
%K nonn
%O 1,2
%A _R. H. Hardin_ May 16 2011
