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A221891 Number of 2 X n arrays of occupancy after each element moves to some horizontal, diagonal or antidiagonal neighbor, without 2-loops or left turns. 1

%I

%S 0,0,8,37,169,811,3878,18502,88302,421463,2011587,9601013,45824300,

%T 218713020,1043886804,4982326441,23779950797,113498396063,

%U 541712050514,2585516235106,12340309202426,58898578606299,281114719650631

%N Number of 2 X n arrays of occupancy after each element moves to some horizontal, diagonal or antidiagonal neighbor, without 2-loops or left turns.

%C Row 2 of A221890.

%H R. H. Hardin, <a href="/A221891/b221891.txt">Table of n, a(n) for n = 1..162</a>

%F Empirical: a(n) = 5*a(n-1) -2*a(n-2) +5*a(n-3) -3*a(n-4).

%F Empirical g.f.: x^3*(8 - 3*x) / (1 - 5*x + 2*x^2 - 5*x^3 + 3*x^4). - _Colin Barker_, Feb 12 2018

%e Some solutions for n=4:

%e ..0..2..0..1....0..2..1..1....0..1..1..0....0..2..3..1....1..2..0..0

%e ..1..1..3..0....1..1..2..0....1..3..2..0....0..1..1..0....0..1..3..1

%K nonn

%O 1,3

%A _R. H. Hardin_, Jan 30 2013

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Last modified August 14 02:34 EDT 2022. Contains 356109 sequences. (Running on oeis4.)