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%I #10 Mar 19 2021 09:13:03
%S 20,105,562,3051,16582,90186,490547,2668340,14514612,78953457,
%T 429474356,2336164666,12707780399,69125130364,376012453568,
%U 2045354053809,11125890031368,60520294171670,329205663240431,1790744248612872
%N 1/4 the number of (n+1)X3 0..3 arrays with every 2X2 subblock having exactly two distinct clockwise edge differences
%C Column 2 of A209553
%H R. H. Hardin, <a href="/A209547/b209547.txt">Table of n, a(n) for n = 1..210</a>
%F Empirical: a(n) = 8*a(n-1) -14*a(n-2) -3*a(n-3) +20*a(n-4) -8*a(n-5) -2*a(n-6)
%e Some solutions for n=4
%e ..1..0..1....2..3..2....0..2..0....1..2..3....0..1..2....1..0..1....2..3..0
%e ..0..1..0....3..2..3....2..0..2....0..1..2....1..2..3....2..3..2....1..0..3
%e ..1..2..3....2..1..0....0..2..0....3..2..3....0..3..2....3..2..3....0..1..2
%e ..0..1..0....1..0..1....2..0..2....0..1..2....3..0..1....2..3..2....3..2..1
%e ..1..0..1....2..3..2....0..2..0....1..2..1....0..3..2....1..0..1....2..3..2
%K nonn
%O 1,1
%A _R. H. Hardin_ Mar 10 2012
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