A127896 - OEIS

A127896

Expansion of 1/(1 + 2*x + 3*x^2 + x^3).

1, -2, 1, 3, -7, 4, 10, -25, 16, 33, -89, 63, 108, -316, 245, 350, -1119, 943, 1121, -3952, 3598, 3539, -13920, 13625, 10971, -48897, 51256, 33208, -171287, 191694, 97265, -598325, 713161, 271388, -2083934

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OFFSET

0,2

COMMENTS

Row sums of A127895. Series reversion is A127897.

LINKS

G. C. Greubel, Table of n, a(n) for n = 0..1000

Paul Barry, Centered polygon numbers, heptagons and nonagons, and the Robbins numbers, arXiv:2104.01644 [math.CO], 2021.

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

FORMULA

a(n) = Sum_{k=0..n} (-1)^(n-k)*C(n+2k+2,n-k).

a(n) = -2*a(n-1) -3*a(n-2) -a(n-3), n>=3. - Vincenzo Librandi, Mar 22 2011

MATHEMATICA

CoefficientList[Series[1/(1+2x+3x^2+x^3), {x, 0, 40}], x] (* Harvey P. Dale, Apr 19 2011 *)

LinearRecurrence[{-2, -3, -1}, {1, -2, 1}, 30] (* G. C. Greubel, Apr 29 2018 *)

PROG

(PARI) x='x+O('x^50); Vec(1/(1+2*x+3*x^2+x^3)) \\ G. C. Greubel, Apr 29 2018

(Magma) I:=[1, -2, 1]; [n le 3 select I[n] else -2*Self(n-1) -3*Self(n-2) -Self(n-3): n in [1..50]]; // G. C. Greubel, Apr 29 2018

CROSSREFS

Cf. A127895, A127897.

Sequence in context: A360587 A058170 A238206 * A010757 A323943 A286616

Adjacent sequences: A127893 A127894 A127895 * A127897 A127898 A127899

KEYWORD

easy,sign

AUTHOR

Paul Barry, Feb 04 2007

STATUS

approved