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A011903
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a(n) = floor(n*(n-1)*(n-2)/21).
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1
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0, 0, 0, 0, 1, 2, 5, 10, 16, 24, 34, 47, 62, 81, 104, 130, 160, 194, 233, 276, 325, 380, 440, 506, 578, 657, 742, 835, 936, 1044, 1160, 1284, 1417, 1558, 1709, 1870, 2040, 2220, 2410, 2611, 2822, 3045, 3280
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OFFSET
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0,6
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LINKS
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Index entries for linear recurrences with constant coefficients, signature (3,-3,1,0,0,0,1,-3,3,-1). [From R. J. Mathar, Apr 15 2010]
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FORMULA
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a(n) = 3*a(n-1) - 3*a(n-2) + a(n-3) + a(n-7) - 3*a(n-8) + 3*a(n-9) - a(n-10).
G.f.: x^4*(x^5-x^4+2*x^2-x+1) / ( (-1+x)^4*(x^6+x^5+x^4+x^3+x^2+x+1) ). (End)
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MATHEMATICA
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CoefficientList[Series[x^4*(x^5-x^4+2*x^2-x+1)/((-1+x)^4*(x^6+x^5+x^4+ 5x^3+x^2+x+1)), {x, 0, 10}], x] (* Vincenzo Librandi, Jul 07 2012 *)
LinearRecurrence[{3, -3, 1, 0, 0, 0, 1, -3, 3, -1}, {0, 0, 0, 0, 1, 2, 5, 10, 16, 24}, 60] (* Harvey P. Dale, May 03 2023 *)
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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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