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A140681
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a(n) = 3*n*(n+6).
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13
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0, 21, 48, 81, 120, 165, 216, 273, 336, 405, 480, 561, 648, 741, 840, 945, 1056, 1173, 1296, 1425, 1560, 1701, 1848, 2001, 2160, 2325, 2496, 2673, 2856, 3045, 3240, 3441, 3648, 3861, 4080, 4305, 4536, 4773, 5016, 5265, 5520, 5781
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OFFSET
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0,2
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LINKS
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FORMULA
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a(n) = A028560(n)*3 = 3*n^2 + 18*n = n*(3*n+18).
G.f.: 3*x*(7 - 5*x)/(1-x)^3.
E.g.f.: 3*x*(x+7)*exp(x). (End)
Sum_{n>=1} 1/a(n) = 49/360.
Sum_{n>=1} (-1)^(n+1)/a(n) = 37/1080. (End)
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MAPLE
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MATHEMATICA
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LinearRecurrence[{3, -3, 1}, {0, 21, 48}, 50] (* Harvey P. Dale, May 03 2023 *)
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PROG
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CROSSREFS
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Cf. A028560, A033428, A045944, A140676, A067725, A140677, A140678, A067707, A140679, A140680, A140689, A000217, A005563, A067728, A140091, A212331.
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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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