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A221673
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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.
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1
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1, 5, 27, 139, 715, 3666, 18787, 96249, 493063, 2525780, 12938520, 66278434, 339515341, 1739187492, 8909090065, 45637335102, 233779915777, 1197551273093, 6134526332322, 31424469370357, 160973679388600, 824597072708976
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OFFSET
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1,2
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COMMENTS
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LINKS
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FORMULA
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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
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EXAMPLE
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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
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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