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A221894
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Number of n X 2 arrays of occupancy after each element stays put or moves to some horizontal, vertical or antidiagonal neighbor, without move-in move-out straight through or left turns.
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1
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3, 31, 266, 2305, 19936, 172624, 1494152, 12933821, 111957318, 969123166, 8388906524, 72615905296, 628576515760, 5441072941952, 47098919537873, 407696835820987, 3529098152699791, 30548517126329090, 264433534642030465
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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) + 26*a(n-2) + 45*a(n-3) + 34*a(n-4) - 2*a(n-5) - 4*a(n-6) + a(n-7).
Empirical g.f.: x*(3 + 16*x + 33*x^2 + 34*x^3 - 2*x^4 - 4*x^5 + x^6) / (1 - 5*x - 26*x^2 - 45*x^3 - 34*x^4 + 2*x^5 + 4*x^6 - x^7). - Colin Barker, Aug 11 2018
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EXAMPLE
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Some solutions for n=3:
..0..2....2..0....1..0....1..2....1..2....0..2....0..0....0..1....1..0....1..0
..2..0....0..1....0..1....0..1....0..1....1..1....3..1....0..3....0..3....1..1
..1..1....1..2....4..0....2..0....1..1....2..0....1..1....2..0....2..0....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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