A209505 - OEIS

%I #8 Jul 10 2018 06:15:48

%S 27,123,561,2559,11673,53247,242889,1107951,5053977,23053983,

%T 105161961,479701839,2188185273,9981522687,45531242889,207693169071,

%U 947403359577,4321630459743,19713345579561,89923466978319,410190643732473

%N Half the number of (n+1) X 3 0..2 arrays with every 2 X 2 subblock having two or four distinct clockwise edge differences.

%C Column 2 of A209511.

%H R. H. Hardin, <a href="/A209505/b209505.txt">Table of n, a(n) for n = 1..210</a>

%F Empirical: a(n) = 5*a(n-1) -2*a(n-2).

%F Empirical g.f.: 3*x*(9 - 4*x) / (1 - 5*x + 2*x^2). - _Colin Barker_, Jul 10 2018

%e Some solutions for n=4:

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

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

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

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

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

%Y Cf. A209511.

%K nonn

%O 1,1

%A _R. H. Hardin_, Mar 09 2012