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A016923
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a(n) = (6*n + 1)^3.
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17
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1, 343, 2197, 6859, 15625, 29791, 50653, 79507, 117649, 166375, 226981, 300763, 389017, 493039, 614125, 753571, 912673, 1092727, 1295029, 1520875, 1771561, 2048383, 2352637, 2685619, 3048625
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OFFSET
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0,2
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REFERENCES
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S. R. Finch, Mathematical Constants, Cambridge, 2003, Section 1.6.3.
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LINKS
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FORMULA
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Sum_{n>=0} 1/a(n) = Pi^3/(36*sqrt(3)) + 91*zeta(3)/216.
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MATHEMATICA
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a[n_]:=(6*n + 1)^3; Array[a, 60, 0] (* or *)
LinearRecurrence[{4, -6, 4, -1}, {1, 343, 2197, 6859}, 60] (* or *)
CoefficientList[Series[(1 + 339 x + 831 x^2 + 125 x^3)/(-1 + x)^4, {x, 0, 60}], x] (* Stefano Spezia, Sep 03 2018 *)
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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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