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A011874
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a(n) = floor(n*(n-1)/21).
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0
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0, 0, 0, 0, 0, 0, 1, 2, 2, 3, 4, 5, 6, 7, 8, 10, 11, 12, 14, 16, 18, 20, 22, 24, 26, 28, 30, 33, 36, 38, 41, 44, 47, 50, 53, 56, 60, 63, 66, 70, 74, 78, 82, 86, 90, 94, 98, 102, 107, 112, 116, 121, 126, 131, 136, 141, 146, 152, 157, 162, 168
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OFFSET
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0,8
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LINKS
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Index entries for linear recurrences with constant coefficients, signature (2,-1,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,1,-2,1).
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FORMULA
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G.f.: x^6*(1-x^2+x^3+x^9-x^10+x^12)/((1-x)^2*(1-x^21)). - R. J. Mathar, Sep 09 2008
a(n) = 2*a(n-1) - a(n-2) + a(n-21) - 2*a(n-22) + a(n-23). - R. J. Mathar, Aug 11 2021
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MATHEMATICA
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CoefficientList[Series[x^6*(1-x^2+x^3+x^9-x^10+x^12) / ((1-x)^2*(1-x^21)), {x, 0, 64}], x] (* Georg Fischer, Aug 15 2021 *)
LinearRecurrence[{2, -1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, -2, 1}, {0, 0, 0, 0, 0, 0, 1, 2, 2, 3, 4, 5, 6, 7, 8, 10, 11, 12, 14, 16, 18, 20, 22}, 70] (* Harvey P. Dale, Feb 24 2023 *)
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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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