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A243038
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Number of length n+3 0..2 arrays with no four elements in a row with pattern abab (with a!=b) and new values 0..2 introduced in 0..2 order.
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1
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13, 36, 101, 285, 806, 2281, 6457, 18280, 51753, 146521, 414826, 1174445, 3325061, 9413836, 26652237, 75457205, 213632718, 604832081, 1712386801, 4848070480, 13725746641, 38860021041, 110019605842, 311485000405, 881869233533
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OFFSET
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1,1
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LINKS
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FORMULA
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Empirical: a(n) = 3*a(n-1) - a(n-3) - a(n-4).
Empirical g.f.: x*(13 - 3*x - 7*x^2 - 5*x^3) / ((1 - x)*(1 - 2*x - 2*x^2 - x^3)). - Colin Barker, Nov 01 2018
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EXAMPLE
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Some solutions for n=4:
..0....0....0....0....0....0....0....0....0....0....0....0....0....0....0....0
..1....1....0....0....0....1....1....1....0....1....1....0....1....1....0....1
..2....2....0....1....1....2....1....1....0....1....1....1....0....2....0....2
..0....0....0....1....2....0....1....0....1....2....2....1....2....0....1....1
..0....1....1....0....2....1....0....1....0....1....1....1....1....2....2....0
..1....0....2....1....1....2....2....2....2....0....1....2....1....1....1....1
..1....2....2....2....2....0....1....1....1....1....2....2....1....0....0....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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