login
This site is supported by donations to The OEIS Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A078712 Series expansion of (-3-2*x)/(1+x-x^3) in powers of x. 4
-3, 1, -1, -2, 3, -4, 2, 1, -5, 7, -6, 1, 6, -12, 13, -7, -5, 18, -25, 20, -2, -23, 43, -45, 22, 21, -66, 88, -67, 1, 87, -154, 155, -68, -86, 241, -309, 223, 18, -327, 550, -532, 205, 345, -877, 1082, -737, -140, 1222, -1959, 1819, -597, -1362 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,1

COMMENTS

This sequence is -A001608(-n), the Perrin sequence for negative n. - T. D. Noe, Oct 10 2006

LINKS

Vincenzo Librandi, Table of n, a(n) for n = 0..1000

Index entries for linear recurrences with constant coefficients, signature (-1,0,1).

FORMULA

a(n) = a(n-3)-a(n-1) with a(0)=-3, a(1)=1, a(2)=-1.

a(n) = A001945(n)-A001608(n).

a(n) ~ 2*real(r^n) with r=0.87744+0.7448617i one inverse complex root of x^3-x-1=0.

2*a(n) = A001608(2*n) - (A001608(n))^2 follows from the Binet formula for a(n) = - p^(-n) - r^(-n) - s^(-n), where p, r, s are roots of the Perrin polynomial x^3 - x - 1. - Roman Witula, Jan 31 2013

G.f.: (2*x+3)/(x^3-x-1). - Vincenzo Librandi, May 17 2013

EXAMPLE

G.f. = -3 + x - x^2 - 2*x^3 + 3*x^4 - 4*x^5 + 2*x^6 + x^7 - 5*x^8 + 7*x^9 + ...

MATHEMATICA

CoefficientList[Series[(2x+3)/(x^3-x-1), {x, 0, 60}], x] (* or *) LinearRecurrence[ {-1, 0, 1}, {-3, 1, -1}, 60] (* Harvey P. Dale, Mar 18 2012 *)

a[ n_] := If[ n < 0, SeriesCoefficient[ (-3 + x^2) / (1 - x^2 - x^3), {x, 0, -n}], SeriesCoefficient[ (-3 - 2 x) / (1 + x - x^3), {x, 0, n}]]; (* Michael Somos, Oct 15 2017 *)

PROG

(PARI) Vec((2*x+3)/(x^3-x-1)+O(x^99)) \\ Charles R Greathouse IV, Sep 26 2012

(PARI) {a(n) = if( n<0, polcoeff( (-3 + x^2) / (1 - x^2 - x^3) + x * O(x^-n), -n), polcoeff( (-3 - 2*x) / (1 + x - x^3) + x * O(x^n), n))}; /* Michael Somos, Oct 15 2017 */

(MAGMA) I:=[-3, 1, -1]; [n le 3 select I[n] else -Self(n-1)+Self(n-3): n in [1..60]]; // Vincenzo Librandi, May 17 2013

CROSSREFS

Cf. A001608, A001945.

Sequence in context: A269973 A128316 A065836 * A287218 A221978 A035254

Adjacent sequences:  A078709 A078710 A078711 * A078713 A078714 A078715

KEYWORD

sign,easy

AUTHOR

Ralf Stephan, Dec 19 2002

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent | More pages
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy .

Last modified February 25 00:39 EST 2018. Contains 299630 sequences. (Running on oeis4.)