A211035 - OEIS

%I #6 Dec 18 2015 18:18:06

%S 1,4,40,800,33432,2888696,517902680,192533704008,148429379845856,

%T 237284500891487840,786611979025079107456,5407447771030956200932952,

%U 77084070831919712319047890192,2278648745820732735808198902023640

%N 1/3 the number of n X n 0..2 symmetric matrices with every element equal to zero or one horizontal or vertical neighbor

%e Some solutions for n=4

%e ..1..0..2..2....2..1..0..0....0..1..0..2....0..1..1..0....1..2..1..0

%e ..0..1..0..0....1..0..2..1....1..2..0..2....1..2..0..2....2..0..1..2

%e ..2..0..1..2....0..2..0..2....0..0..2..0....1..0..2..0....1..1..0..1

%e ..2..0..2..1....0..1..2..0....2..2..0..1....0..2..0..1....0..2..1..0

%K nonn

%O 1,2

%A _R. H. Hardin_ Mar 30 2012