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A014990 a(n) = (1 - (-8)^n)/9. 9
1, -7, 57, -455, 3641, -29127, 233017, -1864135, 14913081, -119304647, 954437177, -7635497415, 61083979321, -488671834567, 3909374676537, -31274997412295, 250199979298361, -2001599834386887, 16012798675095097 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

q-integers for q=-8.

LINKS

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

Index entries for linear recurrences with constant coefficients, signature (-7,8).

FORMULA

a(n) = a(n-1) + q^{(n-1)} = {(q^n - 1) / (q - 1)}

From Philippe Deléham, Feb 13 2007: (Start)

a(1)=1, a(2)=-7, a(n) = -7*a(n-1) + 8*a(n-2) for n > 2.

a(n) = (-1)^(n+1)*A015565(n).

G.f.: x/(1 + 7*x - 8*x^2). (End)

a(n) = (1/9)*(1 + 8*(-8)^n), with n >= 0. - Paolo P. Lava, Nov 21 2008

MAPLE

a:=n->sum ((-8)^j, j=0..n): seq(a(n), n=0..25); # Zerinvary Lajos, Dec 16 2008

MATHEMATICA

QBinomial[Range[20], 1, -8] (* or *) LinearRecurrence[{-7, 8}, {1, -7}, 20] (* Harvey P. Dale, Dec 19 2011 *)

PROG

(Sage) [gaussian_binomial(n, 1, -8) for n in xrange(1, 20)] # Zerinvary Lajos, May 28 2009

(MAGMA) I:=[1, -7]; [n le 2 select I[n] else -7*Self(n-1) +8*Self(n-2): n in [1..30]]; // Vincenzo Librandi, Oct 22 2012

(PARI) a(n)=(1-(-8)^n)/9 \\ Charles R Greathouse IV, Oct 07 2015

CROSSREFS

Cf. A015565, A077925, A014983, A014985, A014986, A014987, A014989, A014991, A014992, A014993, A014994.

Sequence in context: A218587 A218838 A082310 * A015565 A268316 A291537

Adjacent sequences:  A014987 A014988 A014989 * A014991 A014992 A014993

KEYWORD

sign,easy

AUTHOR

Olivier Gérard

EXTENSIONS

Better name from Ralf Stephan, Jul 14 2013

STATUS

approved

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Last modified February 19 18:31 EST 2018. Contains 299356 sequences. (Running on oeis4.)