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A168237 a(n) = (6*n + 3*(-1)^n - 3)/4. 3
0, 3, 3, 6, 6, 9, 9, 12, 12, 15, 15, 18, 18, 21, 21, 24, 24, 27, 27, 30, 30, 33, 33, 36, 36, 39, 39, 42, 42, 45, 45, 48, 48, 51, 51, 54, 54, 57, 57, 60, 60, 63, 63, 66, 66, 69, 69, 72, 72, 75, 75, 78, 78, 81, 81, 84, 84, 87, 87, 90, 90, 93, 93, 96, 96, 99, 99, 102, 102, 105, 105 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

Vincenzo Librandi, Table of n, a(n) for n = 1..1000

Index entries for linear recurrences with constant coefficients, signature (1,1,-1).

FORMULA

a(n) = 3*n - a(n-1) - 3, n>1.

From R. J. Mathar, Jan 05 2011: (Start)

a(n) = 3*A110654(n-1).

G.f.: 3*x^2 / ( (1+x)*(x-1)^2 ). (End)

a(n) = a(n-1) +a(n-2) -a(n-3). - Vincenzo Librandi, Sep 16 2013

E.g.f.: (3/4)*(1 + (2*x - 1)*exp(2*x))*exp(-x). - G. C. Greubel, Jul 16 2016

MATHEMATICA

CoefficientList[Series[3 x/((1 + x) (x - 1)^2), {x, 0, 70}], x] (* Vincenzo Librandi, Sep 16 2013 *)

Table[(6*n + 3*(-1)^n - 3)/4, {n, 1, 50}] (* or *) LinearRecurrence[{1, 1, -1}, {0, 3, 3}, 50] (* G. C. Greubel, Jul 16 2016 *)

PROG

(MAGMA) [3*n/2-3/4+3*(-1)^n/4: n in [1..70]]; // Vincenzo Librandi, Sep 16 2013

CROSSREFS

Cf. A008585.

Sequence in context: A227128 A061795 A110261 * A049318 A079551 A182843

Adjacent sequences:  A168234 A168235 A168236 * A168238 A168239 A168240

KEYWORD

nonn,easy

AUTHOR

Vincenzo Librandi, Nov 21 2009

EXTENSIONS

New definition by R. J. Mathar, Jan 05 2011

STATUS

approved

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Last modified May 22 20:08 EDT 2017. Contains 286906 sequences.