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A243027
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Number of length n+3 0..2 arrays with no four elements in a row with pattern abba (possibly a=b) and new values 0..2 introduced in 0..2 order.
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1
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12, 32, 85, 226, 601, 1598, 4249, 11298, 30041, 79878, 212393, 564746, 1501641, 3992814, 10616761, 28229618, 75061625, 199586390, 530693641, 1411096922, 3752060265, 9976604734, 26527463577, 70535652418, 187551977881, 498694535334
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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) = 2*a(n-1) + a(n-2) + 2*a(n-3).
Empirical g.f.: x*(12 + 8*x + 9*x^2) / (1 - 2*x - x^2 - 2*x^3). - Colin Barker, Nov 01 2018
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EXAMPLE
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Some solutions for n=3:
..0....0....0....0....0....0....0....0....0....0....0....0....0....0....0....0
..0....0....1....1....1....0....1....1....1....1....0....1....1....0....1....1
..1....0....0....0....2....1....2....1....0....2....1....0....1....1....2....0
..2....1....1....1....0....0....2....2....0....1....2....2....1....2....0....1
..1....1....2....1....0....2....2....0....2....1....2....2....2....1....2....2
..0....1....0....1....0....0....0....0....1....1....2....2....2....1....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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