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A211850
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Number of nonnegative integer arrays of length 2n+5 with new values 0 upwards introduced in order, no three adjacent elements all unequal, and containing the value n+1.
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1
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63, 147, 286, 494, 785, 1173, 1672, 2296, 3059, 3975, 5058, 6322, 7781, 9449, 11340, 13468, 15847, 18491, 21414, 24630, 28153, 31997, 36176, 40704, 45595, 50863, 56522, 62586, 69069, 75985, 83348, 91172, 99471, 108259, 117550, 127358, 137697, 148581
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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) = (7/3)*n^3 + (27/2)*n^2 + (163/6)*n + 20.
G.f.: x*(63 - 105*x + 76*x^2 - 20*x^3) / (1 - x)^4.
a(n) = 4*a(n-1) - 6*a(n-2) + 4*a(n-3) - a(n-4) for n>4.
(End)
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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
..1....1....0....1....1....0....0....1....1....1....1....1....1....1....1....1
..1....1....0....1....1....1....1....1....1....1....1....1....1....1....0....0
..1....1....1....2....2....1....1....2....1....2....0....2....2....2....0....0
..2....2....1....2....2....0....2....2....2....2....0....2....2....2....0....0
..2....2....2....3....2....0....2....2....2....3....2....3....3....3....2....2
..2....3....2....3....3....2....3....3....3....2....0....3....3....3....2....2
..3....2....2....4....2....2....2....2....3....2....0....3....1....3....3....3
..2....2....3....4....2....3....2....2....4....4....3....0....1....4....3....3
..2....4....3....3....4....3....2....4....4....4....3....0....1....4....3....4
..4....4....4....3....2....4....4....4....2....0....4....4....4....5....4....4
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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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