%I #4 Mar 31 2012 12:37:34
%S 1,6,70,1584,69094,5804980,937523156,290938653352,173346851987198
%N 1/3 the number of (2n)X(2n) 0..2 symmetric matrices with every element equal to two horizontal and vertical neighbors
%e Some solutions for n=2
%e ..2..2..0..0....1..1..0..0....0..0..0..0....0..0..2..2....2..2..1..1
%e ..2..2..0..0....1..1..0..0....0..1..1..0....0..0..2..2....2..2..1..1
%e ..0..0..1..1....0..0..2..2....0..1..1..0....2..2..0..0....1..1..0..0
%e ..0..0..1..1....0..0..2..2....0..0..0..0....2..2..0..0....1..1..0..0
%K nonn
%O 1,2
%A _R. H. Hardin_ Mar 30 2012