%I #10 Jul 13 2018 05:33:13
%S 30,204,1380,9348,63300,428676,2902980,19659012,133130820,901562244,
%T 6105381060,41345652228,279992833860,1896111996036,12840473986500,
%U 86955713884932,588864257262660,3987789852932484,27005320351814340
%N Half the number of (n+1) X 2 0..2 arrays with every 2 X 2 subblock having exactly one duplicate clockwise edge difference.
%C Column 1 of A209796.
%H R. H. Hardin, <a href="/A209789/b209789.txt">Table of n, a(n) for n = 1..210</a>
%F Empirical: a(n) = 5*a(n-1) + 12*a(n-2).
%F Conjectures from _Colin Barker_, Jul 13 2018: (Start)
%F G.f.: 6*x*(5 + 9*x) / (1 - 5*x - 12*x^2).
%F a(n) = (2^(-2-n)*(3*(5+sqrt(73))^n*(25+3*sqrt(73)) + (5-sqrt(73))^n*(-75+9*sqrt(73)))) / sqrt(73).
%F (End)
%e Some solutions for n=4:
%e ..2..0....1..2....0..1....1..1....2..1....2..1....2..1....0..0....0..2....1..2
%e ..1..0....0..2....2..1....2..0....1..1....0..0....0..0....2..1....2..2....0..2
%e ..0..0....2..2....1..1....0..0....0..1....2..0....1..1....2..0....0..1....0..2
%e ..1..0....2..0....2..0....2..2....2..2....0..0....1..0....1..0....0..1....2..2
%e ..2..2....0..0....0..0....2..1....1..2....1..0....2..2....0..0....1..1....0..2
%Y Cf. A209796.
%K nonn
%O 1,1
%A _R. H. Hardin_, Mar 13 2012