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A011897
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a(n) = floor(n*(n-1)*(n-2)/15).
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1
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0, 0, 0, 0, 1, 4, 8, 14, 22, 33, 48, 66, 88, 114, 145, 182, 224, 272, 326, 387, 456, 532, 616, 708, 809, 920, 1040, 1170, 1310, 1461, 1624, 1798, 1984, 2182, 2393, 2618, 2856, 3108, 3374, 3655, 3952, 4264, 4592
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OFFSET
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0,6
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LINKS
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FORMULA
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a(n) = 3*a(n-1) - 3*a(n-2) + a(n-3) + a(n-5) - 3*a(n-6) + 3*a(n-7) - a(n-8).
G.f.: x^4*(x^3-x^2+x+1) / ( (-1+x)^4*(x^4+x^3+x^2+x+1) ). (End)
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MATHEMATICA
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CoefficientList[Series[x^4(x^3-x^2+x+1)/((-1+x)^4(x^4+x^3+x^2+x+1)), {x, 0, 45}], x] (* Harvey P. Dale, Feb 25 2011 *)
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PROG
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CROSSREFS
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KEYWORD
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nonn,easy
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AUTHOR
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STATUS
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approved
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