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A221673 Number of n X 2 arrays of occupancy after each element moves to some horizontal or vertical neighbor, without move-in move-out left turns. 1
1, 5, 27, 139, 715, 3666, 18787, 96249, 493063, 2525780, 12938520, 66278434, 339515341, 1739187492, 8909090065, 45637335102, 233779915777, 1197551273093, 6134526332322, 31424469370357, 160973679388600, 824597072708976 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Column 2 of A221676.

LINKS

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

FORMULA

Empirical: a(n) = 7*a(n-1) - 9*a(n-2) - 5*a(n-3) + 10*a(n-4) - 3*a(n-5).

Empirical g.f.: x*(1 - x)^2 / (1 - 7*x + 9*x^2 + 5*x^3 - 10*x^4 + 3*x^5). - Colin Barker, Aug 10 2018

EXAMPLE

Some solutions for n=3:

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

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

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

CROSSREFS

Cf. A221676.

Sequence in context: A198771 A084177 A037675 * A257061 A052225 A293295

Adjacent sequences:  A221670 A221671 A221672 * A221674 A221675 A221676

KEYWORD

nonn

AUTHOR

R. H. Hardin, Jan 21 2013

STATUS

approved

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Last modified February 22 18:24 EST 2020. Contains 332148 sequences. (Running on oeis4.)