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A250346
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Number of length n arrays x(i), i=1..n with x(i) in i..i+3 and no value appearing more than 2 times.
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2
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4, 16, 62, 235, 888, 3349, 12620, 47545, 179104, 674666, 2541362, 9572864, 36059224, 135828387, 511640114, 1927252354, 7259597884, 27345542237, 103005522894, 388002462425, 1461532415920, 5505318159061, 20737499694808, 78114267177504
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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) = 4*a(n-1) - 2*a(n-3) - 5*a(n-4) + a(n-6).
Empirical g.f.: x*(4 - 2*x^2 - 5*x^3 + x^5) / (1 - 4*x + 2*x^3 + 5*x^4 - x^6). - Colin Barker, Nov 12 2018
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EXAMPLE
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Some solutions for n=6:
..3....1....1....1....3....1....1....0....3....2....1....2....0....1....0....0
..2....2....3....4....2....1....4....4....4....2....3....4....2....2....3....1
..5....4....2....2....3....4....2....3....2....4....3....5....2....2....4....2
..4....5....3....4....6....6....6....3....6....5....4....5....6....3....3....4
..5....4....4....7....4....5....5....5....5....4....6....7....7....5....7....5
..6....5....5....5....6....8....5....5....5....5....7....7....6....6....8....5
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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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