%I #8 Mar 09 2015 04:28:03
%S 1,2,5,25,205,2849,66677,2633485,175143651,19638725775,3710411382331,
%T 1181447019186469,633957805831439213,573281808520220290885,
%U 873645764409736229092874,2243689725607702437916265557
%N Number of n X n symmetric binary matrices containing no more than two 1s in any 2 X 2 sub-block.
%H R. H. Hardin, May 31 2008, <a href="/A139007/b139007.txt">Table of n, a(n) for n = 0..20</a>
%K nonn
%O 0,2
%A _R. H. Hardin_, May 31 2008