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A222439
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Number of n X 3 0..3 arrays with entries increasing mod 4 by 0, 1 or 2 rightwards and downwards, starting with upper left zero.
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2
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9, 147, 2403, 39285, 642249, 10499787, 171655443, 2806303725, 45878770089, 750047661027, 12262131106083, 200467073061765, 3277329775247529, 53579324981787867, 875939945740498323, 14320277248820697405
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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) = 18*a(n-1) - 27*a(n-2).
Empirical g.f.: 3*x*(3 - 5*x) / (1 - 18*x + 27*x^2). - Colin Barker, Mar 15 2018
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EXAMPLE
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Some solutions for n=3:
..0..2..3....0..1..2....0..2..2....0..2..3....0..0..0....0..2..2....0..0..1
..2..0..0....2..2..0....1..2..2....2..0..0....0..2..2....0..0..2....2..0..2
..2..0..1....2..0..1....3..3..3....2..0..2....0..2..3....1..2..2....3..1..2
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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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