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%I #9 Jul 13 2018 08:19:22
%S 62,562,5008,44770,399930,3573388,31926146,285247762,2548561164,
%T 22770302450,203442764450,1817673135676,16240122477074,
%U 145098465897778,1296391988417932,11582701309989362,103486422895200258
%N Half the number of (n+1) X 2 0..3 arrays with every 2 X 2 subblock having two or four distinct clockwise edge differences.
%C Column 1 of A209913.
%H R. H. Hardin, <a href="/A209906/b209906.txt">Table of n, a(n) for n = 1..210</a>
%F Empirical: a(n) = 7*a(n-1) + 21*a(n-2) - 30*a(n-3) - 30*a(n-4) + 12*a(n-5) + 8*a(n-6).
%F Empirical g.f.: 2*x*(31 + 64*x - 114*x^2 - 114*x^3 + 46*x^4 + 32*x^5) / (1 - 7*x - 21*x^2 + 30*x^3 + 30*x^4 - 12*x^5 - 8*x^6). - _Colin Barker_, Jul 13 2018
%e Some solutions for n=4:
%e ..0..2....1..2....0..2....2..0....0..0....0..0....3..0....2..0....2..3....1..0
%e ..0..3....0..3....3..3....2..3....1..3....2..3....1..0....3..0....0..1....0..1
%e ..0..1....2..2....0..1....1..2....2..1....3..2....0..3....2..0....2..0....0..3
%e ..2..3....0..3....2..3....0..1....3..2....0..1....2..3....3..1....0..1....1..2
%e ..1..2....2..2....2..0....1..2....0..3....0..3....1..2....1..2....3..0....2..1
%Y Cf. A209913.
%K nonn
%O 1,1
%A _R. H. Hardin_, Mar 15 2012
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