A209506 - OEIS

%I #8 Jul 10 2018 13:58:52

%S 81,561,3906,27225,189801,1323270,9225765,64321641,448447914,

%T 3126561201,21798261945,151976626974,1059575080797,7387315894233,

%U 51504076597986,359084401453161,2503522359474057,17454459673057014,121691808074121237

%N Half the number of (n+1) X 4 0..2 arrays with every 2 X 2 subblock having two or four distinct clockwise edge differences.

%C Column 3 of A209511.

%H R. H. Hardin, <a href="/A209506/b209506.txt">Table of n, a(n) for n = 1..210</a>

%F Empirical: a(n) = 9*a(n-1) - 15*a(n-2) + 6*a(n-3).

%F Empirical g.f.: 3*x*(27 - 56*x + 24*x^2) / (1 - 9*x + 15*x^2 - 6*x^3). - _Colin Barker_, Jul 10 2018

%e Some solutions for n=4:

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

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

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

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

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

%Y Cf. A209511.

%K nonn

%O 1,1

%A _R. H. Hardin_, Mar 09 2012