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A011880
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a(n) = floor(n*(n-1)/27).
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1
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0, 0, 0, 0, 0, 0, 1, 1, 2, 2, 3, 4, 4, 5, 6, 7, 8, 10, 11, 12, 14, 15, 17, 18, 20, 22, 24, 26, 28, 30, 32, 34, 36, 39, 41, 44, 46, 49, 52, 54, 57, 60, 63, 66, 70, 73, 76, 80, 83, 87, 90, 94, 98, 102, 106, 110, 114, 118, 122, 126, 131, 135, 140, 144, 149, 154, 158, 163, 168, 173
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OFFSET
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0,9
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LINKS
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Index entries for linear recurrences with constant coefficients, signature (2, -1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, -2, 1).
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FORMULA
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G.f.: x^6(1-x^3+x^5+x^11-x^13+x^16)(1-x^6)/((1-x)(1-x^2)(1-x^3)(1-x^27)).
a(n)= +2*a(n-1) -a(n-2) +a(n-27) -2*a(n-28) +a(n-29). - R. J. Mathar, Aug 11 2021
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MAPLE
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MATHEMATICA
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CoefficientList[Series[x^6 (1 - x^3 + x^5 + x^11 - x^13 + x^16) (1 - x^6)/((1 - x) (1 - x^2) (1 - x^3) (1 - x^27)), {x, 0, 70}], x] (* Vincenzo Librandi, Mar 28 2014 *)
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PROG
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(PARI) a(n)=(n^2-n)\27
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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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EXTENSIONS
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STATUS
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approved
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