%I

%S 1,4,28,342,8170,388316,35871274,6434968504,2248575047080,

%T 1530856226085764,2029777404349820818,5241143888167535563974,

%U 26356732501074298121803368,258136468277025366420232101764

%N Number of n X n symmetric binary matrices with every 1 adjacent to another 1 horizontally or vertically.

%K nonn

%O 1,2

%A _R. H. Hardin_, Jun 18 2008