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A152728 a(n) + a(n+1) + a(n+2) = n^3. 6
0, 0, 0, 1, 7, 19, 38, 68, 110, 165, 237, 327, 436, 568, 724, 905, 1115, 1355, 1626, 1932, 2274, 2653, 3073, 3535, 4040, 4592, 5192, 5841, 6543, 7299, 8110, 8980, 9910, 10901, 11957, 13079, 14268, 15528, 16860, 18265, 19747, 21307, 22946, 24668, 26474 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,5

COMMENTS

The differences between the terms are (1) a(3*k) - a(3*k-1) = 9*k*(k-1)+1; (2) otherwise, a(n) - a(n-1) = (n-2)*(n-1). - J. M. Bergot, Jul 10 2013

Second differences give A047266. - J. M. Bergot, Dec 01 2014

LINKS

G. C. Greubel, Table of n, a(n) for n = 0..5000

Index entries for linear recurrences with constant coefficients, signature (3,-3,2,-3,3,-1).

FORMULA

From R. J. Mathar, Aug 15 2010: (Start)

a(n) = ( (n-1)*(n^2-2*n-1) - A057078(n))/3.

G.f.: x^3*(1+4*x+x^2) / ( (1+x+x^2)*(x-1)^4 ). (End)

a(n) = 3*a(n-1) - 3*a(n-2) + 2*a(n-3) - 3*a(n-4) + 3*a(n-5) - a(n-5). - Charles R Greathouse IV, Jul 10 2013

a(3n) = n*(9n^2-9n+1), a(3n+1) = n*(9n^2-2), a(3n+2) = n*(9n^2+9n+1). - Ralf Stephan, Jul 12 2013

a(n) = ceiling((n^3 - 3*n^2 + n)/3). - Robert Israel, Dec 01 2014

MAPLE

seq(ceil((n^3 - 3*n^2 + n)/3), n=0..100); # Robert Israel, Dec 01 2014

MATHEMATICA

k0=k1=0; lst={k0, k1}; Do[kt=k1; k1=n^3-k1-k0; k0=kt; AppendTo[lst, k1], {n, 1, 4!}]; lst

LinearRecurrence[{3, -3, 2, -3, 3, -1}, {0, 0, 0, 1, 7, 19}, 50] (* G. C. Greubel, Sep 01 2018 *)

PROG

(PARI) x='x+O('x^50); concat([0, 0, 0], Vec(x^3*(1+4*x+x^2)/((1+x+x^2)*(x -1)^4 ))) \\ G. C. Greubel, Sep 01 2018

(MAGMA) m:=50; R<x>:=PowerSeriesRing(Integers(), m); [0, 0, 0] cat Coefficients(R!(x^3*(1+4*x+x^2)/((1+x+x^2)*(x-1)^4))); // G. C. Greubel, Sep 01 2018

CROSSREFS

Cf. A000578, A047266.

Sequence in context: A027452 A051937 A119327 * A252789 A099061 A078163

Adjacent sequences:  A152725 A152726 A152727 * A152729 A152730 A152731

KEYWORD

nonn,easy

AUTHOR

Vladimir Joseph Stephan Orlovsky, Dec 11 2008

STATUS

approved

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Last modified August 20 23:38 EDT 2019. Contains 326155 sequences. (Running on oeis4.)