%I #5 Dec 18 2015 18:18:07
%S 1,10,228,12627,1667397,527301810,398763964407,721357961638581,
%T 3121075294380253308,32298409320629884228245,
%U 799420627577762936976169203
%N 1/4 the number of n X n 0..3 symmetric matrices with every element equal to zero or two horizontal and vertical neighbors
%e Some solutions for n=4
%e ..0..1..3..0....3..1..2..0....0..3..1..2....2..0..3..1....0..3..0..2
%e ..1..3..1..2....1..2..1..2....3..1..2..0....0..1..2..0....3..0..3..0
%e ..3..1..2..3....2..1..2..0....1..2..1..3....3..2..0..1....0..3..2..1
%e ..0..2..3..0....0..2..0..2....2..0..3..2....1..0..1..2....2..0..1..3
%K nonn
%O 1,2
%A _R. H. Hardin_ Mar 31 2012