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A239024
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Number of n X 2 0..2 arrays with no element equal to the sum of elements to its left or one plus the sum of elements above it, modulo 3.
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1
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1, 3, 4, 11, 16, 43, 64, 171, 256, 683, 1024, 2731, 4096, 10923, 16384, 43691, 65536, 174763, 262144, 699051, 1048576, 2796203, 4194304, 11184811, 16777216, 44739243, 67108864, 178956971, 268435456, 715827883, 1073741824, 2863311531, 4294967296
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OFFSET
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1,2
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LINKS
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FORMULA
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Empirical: a(n) = 5*a(n-2) - 4*a(n-4).
G.f.: x*(1 + 3*x - x^2 - 4*x^3) / ((1 - x)*(1 + x)*(1 - 2*x)*(1 + 2*x)).
a(n) = (2 + (-2)^n + 2*(-1)^n + 7*2^n) / 12.
(End)
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EXAMPLE
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Some solutions for n=5:
..2..0....2..0....2..0....2..0....2..0....2..0....2..0....2..0....2..0....2..0
..1..0....2..0....2..0....2..0....1..2....1..0....1..0....2..0....2..0....1..0
..2..0....1..2....1..0....1..2....2..1....2..0....2..0....1..2....1..2....2..0
..2..0....2..1....1..0....1..2....1..0....1..0....1..2....2..1....1..2....2..0
..1..2....1..2....2..0....2..1....2..0....2..0....2..1....1..0....2..0....1..0
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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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