%I
%S 2,8,52,528,11275,435987,30448860,3920809305,920775496348,
%T 394837552267029,310020405028212730,445022535834699088455,
%U 1167728276848286755937076,5603048100640429152817307256
%N Number of n X n symmetric binary matrices with each 1 adjacent to no more than 2 diagonally or antidiagonally neighboring 1s
%H R. H. Hardin, <a href="/A191552/b191552.txt">Table of n, a(n) for n = 1..24</a>
%e Some solutions for n=4
%e ..1..1..0..0....0..0..0..1....1..1..0..0....0..0..0..0....1..0..1..0
%e ..1..1..1..0....0..0..0..1....1..1..1..0....0..0..1..0....0..0..1..0
%e ..0..1..0..0....0..0..1..0....0..1..1..0....0..1..1..1....1..1..1..1
%e ..0..0..0..1....1..1..0..0....0..0..0..0....0..0..1..1....0..0..1..1
%K nonn
%O 1,1
%A _R. H. Hardin_ Jun 05 2011
