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%I #9 Jul 14 2018 02:47:50
%S 71,567,4521,36057,287559,2293335,18289737,145863801,1163288871,
%T 9277428663,73989087849,590075690265,4705955031303,37530800068887,
%U 299314580024457,2387085211367865,19037414768987367,151826654264588919
%N Number of (n+1) X 2 0..2 arrays with every 2 X 2 subblock having one, three or four distinct clockwise edge differences.
%C Column 1 of A209960.
%H R. H. Hardin, <a href="/A209953/b209953.txt">Table of n, a(n) for n = 1..210</a>
%F Empirical: a(n) = 6*a(n-1) + 15*a(n-2) + 6*a(n-3).
%F Empirical g.f.: x*(71 + 141*x + 54*x^2) / (1 - 6*x - 15*x^2 - 6*x^3). - _Colin Barker_, Jul 14 2018
%e Some solutions for n=4:
%e ..1..1....0..2....0..1....2..1....2..1....2..1....1..2....1..2....1..2....2..1
%e ..0..0....2..1....2..0....0..2....0..2....0..0....0..2....1..1....0..2....2..2
%e ..2..0....0..1....1..2....1..1....2..1....1..1....2..1....1..1....0..2....1..2
%e ..0..0....0..1....2..0....1..2....0..2....1..0....2..0....1..0....2..2....0..2
%e ..0..0....1..1....0..1....1..1....1..0....2..2....0..1....1..2....0..2....2..2
%Y Cf. A209960.
%K nonn
%O 1,1
%A _R. H. Hardin_, Mar 16 2012
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