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A006124 a(n) = 3 + n/2 + 7n^2/2. 1
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 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,1

LINKS

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).

FORMULA

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

MATHEMATICA

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 *)

PROG

(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

CROSSREFS

Sequence in context: A102329 A069143 A097007 * A197182 A074587 A208715

Adjacent sequences:  A006121 A006122 A006123 * A006125 A006126 A006127

KEYWORD

nonn,easy

AUTHOR

N. J. A. Sloane.

STATUS

approved

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Last modified April 23 18:15 EDT 2019. Contains 322387 sequences. (Running on oeis4.)