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A006124
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a(n) = 3 + n/2 + 7n^2/2.
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1
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3, 7, 18, 36, 61, 93, 132, 178, 231, 291, 358, 432, 513, 601, 696, 798, 907, 1023, 1146, 1276, 1413, 1557, 1708, 1866, 2031, 2203, 2382, 2568, 2761, 2961, 3168, 3382, 3603, 3831, 4066, 4308, 4557, 4813
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OFFSET
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0,1
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LINKS
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Vincenzo Librandi, Table of n, a(n) for n = 0..1000
C. L. Mallows & N. J. A. Sloane, Emails, May 1991
C. L. Mallows & N. J. A. Sloane, Emails, Jun. 1991
Index entries for linear recurrences with constant coefficients, signature (3,-3,1).
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FORMULA
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G.f.: (3-2*x+6*x^2)/(1-x)^3. - Vincenzo Librandi, Jul 07 2012
a(n) = 3*a(n-1) -3*a(n-2) +a(n-3). - Vincenzo Librandi, Jul 07 2012
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MATHEMATICA
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Table[3+n/2+7/2 n^2, {n, 0, 50}] (* Harvey P. Dale, Mar 21 2011 *)
CoefficientList[Series[(3-2*x+6*x^2)/(1-x)^3, {x, 0, 50}], x] (* Vincenzo Librandi, Jul 07 2012 *)
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PROG
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(MAGMA) I:=[3, 7, 18]; [n le 3 select I[n] else 3*Self(n-1)-3*Self(n-2)+Self(n-3): n in [1..50]]; // Vincenzo Librandi, Jul 07 2012
(PARI) a(n)=3+n/2+7*n^2/2 \\ Charles R Greathouse IV, Jun 17 2017
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CROSSREFS
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Sequence in context: A102329 A069143 A097007 * A197182 A074587 A208715
Adjacent sequences: A006121 A006122 A006123 * A006125 A006126 A006127
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KEYWORD
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nonn,easy
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AUTHOR
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N. J. A. Sloane.
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STATUS
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approved
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