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A190039
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Number of nondecreasing arrangements of n+2 numbers in 0..7 with the last equal to 7 and each after the second equal to the sum of one or two of the preceding three.
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1
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11, 17, 22, 31, 43, 60, 80, 100, 120, 140, 160, 180, 200, 220, 240, 260, 280, 300, 320, 340, 360, 380, 400, 420, 440, 460, 480, 500, 520, 540, 560, 580, 600, 620, 640, 660, 680, 700, 720, 740, 760, 780, 800, 820, 840, 860, 880, 900, 920, 940, 960, 980, 1000, 1020
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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) = 20*n - 60 for n>5.
G.f.: x*(11 - 5*x - x^2 + 4*x^3 + 3*x^4 + 5*x^5 + 3*x^6) / (1 - x)^2.
a(n) = 2*a(n-1) - a(n-2) for n>7.
(End)
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EXAMPLE
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Some solutions for n=3:
3 1 1 6 7 2 1 1 2 0 2 1 1 2 5 3
4 6 3 7 7 3 3 3 5 7 5 6 2 7 7 4
7 7 4 7 7 5 4 4 7 7 5 6 3 7 7 4
7 7 5 7 7 7 4 7 7 7 7 7 4 7 7 7
7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7
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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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