A211047 - OEIS

%I #5 Dec 18 2015 18:18:07

%S 0,1,4,102,3452,306196,56305300,23135879808,20936361314520,

%T 41767961477927304,184066448459881652770,1789009177710334924490408

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

%e Some solutions for n=4

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

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

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

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

%K nonn

%O 1,3

%A _R. H. Hardin_ Mar 30 2012