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A221731
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Number of n X 2 arrays of occupancy after each element stays put or moves to some horizontal or antidiagonal neighbor, without move-in move-out left turns.
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2
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3, 17, 91, 489, 2627, 14113, 75819, 407321, 2188243, 11755857, 63155771, 339290569, 1822764387, 9792403073, 52607544139, 282622526841, 1518327722483, 8156883666097, 43821073775451, 235419136209449, 1264737828598147
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OFFSET
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1,1
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COMMENTS
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LINKS
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FORMULA
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Empirical: a(n) = 5*a(n-1) + 2*a(n-2).
G.f.: x*(3 + 2*x) / (1 - 5*x - 2*x^2).
a(n) = (2^(-1-n)*((5-sqrt(33))^n*(-1+sqrt(33)) + (1+sqrt(33))*(5+sqrt(33))^n)) / sqrt(33).
(End)
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EXAMPLE
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Some solutions for n=3:
..2..0....1..0....1..0....0..2....0..2....0..2....2..0....1..1....1..0....2..0
..2..0....3..0....3..0....2..0....1..2....0..2....1..1....2..0....2..2....0..1
..0..2....1..1....0..2....2..0....0..1....2..0....2..0....0..2....0..1....2..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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