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A221821 Number of n X 2 arrays of occupancy after each element stays put or moves to some horizontal or vertical neighbor, without consecutive moves in the same direction. 1
3, 31, 252, 2113, 17684, 147920, 1237439, 10351593, 86594795, 724396370, 6059833949, 50692672540, 424062286786, 3547432284249, 29675536361423, 248246446379403, 2076670068892280, 17372085836189001, 145323694322280832 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Column 2 of A221824.

LINKS

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

FORMULA

Empirical: a(n) = 9*a(n-1) - 4*a(n-2) - 11*a(n-3) - 2*a(n-4) + 22*a(n-5) - 16*a(n-6) + 8*a(n-7).

Empirical g.f.: x*(3 + 4*x - 15*x^2 + 2*x^3 + 22*x^4 - 16*x^5 + 8*x^6) / (1 - 9*x + 4*x^2 + 11*x^3 + 2*x^4 - 22*x^5 + 16*x^6 - 8*x^7). - Colin Barker, Aug 11 2018

EXAMPLE

Some solutions for n=3:

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

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

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

CROSSREFS

Cf. A221824.

Sequence in context: A334980 A111400 A057972 * A198852 A114849 A221899

Adjacent sequences: A221818 A221819 A221820 * A221822 A221823 A221824

KEYWORD

nonn

AUTHOR

R. H. Hardin, Jan 26 2013

STATUS

approved

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Last modified December 5 02:30 EST 2022. Contains 358572 sequences. (Running on oeis4.)