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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
0, 0, 8, 37, 169, 811, 3878, 18502, 88302, 421463, 2011587, 9601013, 45824300, 218713020, 1043886804, 4982326441, 23779950797, 113498396063, 541712050514, 2585516235106, 12340309202426, 58898578606299, 281114719650631 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

COMMENTS

Row 2 of A221890.

LINKS

R. H. Hardin, Table of n, a(n) for n = 1..162

FORMULA

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

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

EXAMPLE

Some solutions for n=4:

..0..2..0..1....0..2..1..1....0..1..1..0....0..2..3..1....1..2..0..0

..1..1..3..0....1..1..2..0....1..3..2..0....0..1..1..0....0..1..3..1

CROSSREFS

Sequence in context: A111645 A272739 A220917 * A221063 A221633 A201452

Adjacent sequences:  A221888 A221889 A221890 * A221892 A221893 A221894

KEYWORD

nonn

AUTHOR

R. H. Hardin, Jan 30 2013

STATUS

approved

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Last modified July 4 20:49 EDT 2022. Contains 355086 sequences. (Running on oeis4.)