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%I #8 Jun 13 2018 12:00:06
%S 50,170,558,1906,6386,21940,74714,258496,891586,3106540,10821426,
%T 37946232,133190826,469570860,1657721338,5869905680,20812541098,
%U 73947974244,263041695362,937043382992,3341162160402,11925776401308
%N Number of (n+1) X 2 0..2 arrays with every 2 X 2 subblock having nonzero determinant and having the same number of clockwise edge increases as its horizontal and vertical neighbors.
%C Column 1 of A206128.
%H R. H. Hardin, <a href="/A206121/b206121.txt">Table of n, a(n) for n = 1..210</a>
%F Empirical: a(n) = 2*a(n-1) + 13*a(n-2) - 9*a(n-3) - 50*a(n-4) - 43*a(n-5) + 4*a(n-6) - 4*a(n-8) for n>9.
%F Empirical g.f.: 2*x*(25 + 35*x - 216*x^2 - 485*x^3 - 325*x^4 + 31*x^5 - 10*x^6 - 32*x^7 - x^8) / ((1 - 8*x^2 - 4*x^3)*(1 - 2*x - 5*x^2 - 3*x^3 + 2*x^4 - x^5)). - _Colin Barker_, Jun 13 2018
%e Some solutions for n=4:
%e ..1..2....1..1....2..0....0..1....2..0....0..1....2..1....2..1....1..0....1..1
%e ..0..2....0..1....1..2....2..2....2..1....2..1....2..2....0..2....1..2....2..1
%e ..2..0....1..1....0..2....1..0....0..2....0..2....2..0....1..0....1..1....1..1
%e ..0..1....0..1....2..0....2..1....1..0....1..0....2..2....2..1....0..1....1..2
%e ..2..1....1..1....2..1....1..2....2..1....2..1....1..2....1..0....1..1....1..1
%Y Cf. A206128.
%K nonn
%O 1,1
%A _R. H. Hardin_, Feb 04 2012
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