%I
%S 4,12,72,720,10800,259200,10368000,673920000,70087680000,
%T 11774730240000,3214501355520000,1420809599139840000,
%U 1014458053785845760000,1171699052122651852800000,2191077227469358964736000000
%N Number of (n+1)X(n+1) symmetric binary matrices without the pattern 1 1 antidiagonally
%H R. H. Hardin, <a href="/A190340/b190340.txt">Table of n, a(n) for n = 1..47</a>
%e Some solutions for 3X3
%e ..1..0..1....0..0..1....0..0..1....0..0..0....1..0..0....1..0..1....0..0..0
%e ..0..0..0....0..0..0....0..0..0....0..1..0....0..1..0....0..0..0....0..0..0
%e ..1..0..0....1..0..1....1..0..0....0..0..1....0..0..0....1..0..1....0..0..0
%K nonn
%O 1,1
%A _R. H. Hardin_ May 09 2011
