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A221425 Number of n X 2 arrays of occupancy after each element moves to some horizontal or vertical neighbor, without consecutive moves in the same direction. 1
1, 9, 42, 217, 1116, 5722, 29383, 150821, 774219, 3974308, 20401353, 104726538, 537593996, 2759637891, 14166083083, 72718928341, 373288968420, 1916208848267, 9836498426064, 50493818235236, 259200537583569, 1330557304472777 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Column 2 of A221429.

LINKS

R. H. Hardin, Table of n, a(n) for n = 1..210

FORMULA

Empirical: a(n) = 4*a(n-1) + 6*a(n-2) - 5*a(n-4) + a(n-5).

Empirical g.f.: x*(1 + 5*x - 5*x^3 + x^4) / (1 - 4*x - 6*x^2 + 5*x^4 - x^5). - Colin Barker, Aug 05 2018

EXAMPLE

Some solutions for n=3:

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

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

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

CROSSREFS

Cf. A221429.

Sequence in context: A268622 A289364 A074443 * A007227 A224836 A195975

Adjacent sequences:  A221422 A221423 A221424 * A221426 A221427 A221428

KEYWORD

nonn

AUTHOR

R. H. Hardin, Jan 15 2013

STATUS

approved

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Last modified May 26 15:29 EDT 2019. Contains 323597 sequences. (Running on oeis4.)