The OEIS is supported by the many generous donors to the OEIS Foundation.
%I #5 Dec 18 2015 18:18:06
%S 1,4,40,928,45128,4945168,1207742160,655725571768,791701825710768,
%T 2127149017683661104,12717092443922120808584,
%U 169157473880575759274475472,5006302388939519643670779061032
%N 1/3 the number of n X n 0..2 symmetric matrices with every element equal to zero, one or three horizontal and vertical neighbors
%e Some solutions for n=4
%e ..2..1..2..2....0..1..0..2....1..0..0..1....2..0..2..1....1..0..1..0
%e ..1..0..1..1....1..2..0..1....0..1..2..1....0..1..0..0....0..2..0..2
%e ..2..1..0..2....0..0..2..1....0..2..0..2....2..0..2..1....1..0..2..1
%e ..2..1..2..0....2..1..1..2....1..1..2..0....1..0..1..0....0..2..1..2
%K nonn
%O 1,2
%A _R. H. Hardin_ Mar 30 2012