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A125905 a(0)=1, a(1)=-4, a(n)=-4*a(n-1)-a(n-2) for n>1. 4
1, -4, 15, -56, 209, -780, 2911, -10864, 40545, -151316, 564719, -2107560, 7865521, -29354524, 109552575, -408855776, 1525870529, -5694626340, 21252634831, -79315912984, 296011017105, -1104728155436, 4122901604639, -15386878263120, 57424611447841 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

COMMENTS

Pisano period lengths: 1, 2, 3, 4, 6, 6, 8, 4, 9, 6, 5, 12, 12, 8, 6, 8, 9, 18, 10, 12,... - R. J. Mathar, Aug 10 2012

In engineering literature, these numbers are known as Clapeyron numbers, or Clapeyron's numbers, or Clapeyronian numbers, on account of their appearance in Benoît Clapeyron's influential study (1857) of the bending forces imposed upon multiple supports of a horizontal beam. - John Blythe Dobson, Mar 12 2014

LINKS

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

[Benoît] Clapeyron, Calcul d'une poutre élastique reposant librement sur des appuis inégalement espacés, Comptes rendus hebdomadaires des séances de l'Académie des Sciences, 45 (1857), 1076-1080.

Index entries for linear recurrences with constant coefficients, signature (-4,-1).

FORMULA

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

a(n) = (-1)^n*A001353(n+1) = (-1)^(n+1)*A106707(n+1).

MATHEMATICA

CoefficientList[Series[1/(1+4*x+x^2), {x, 0, 50}], x] (* Vincenzo Librandi, Jun 28 2012 *)

PROG

(MAGMA) I:=[1, -4]; [n le 2 select I[n] else -4*Self(n-1)-Self(n-2): n in [1..30]]; // Vincenzo Librandi, Jun 28 2012

CROSSREFS

Cf. A001353, A106707.

Sequence in context: A001353 A106707 * A195503 A010905 A026030 A047038

Adjacent sequences:  A125902 A125903 A125904 * A125906 A125907 A125908

KEYWORD

easy,sign

AUTHOR

Philippe Deléham, Feb 04 2007

EXTENSIONS

Typo in a(22) corrected - Neven Juric, Dec 20 2010

STATUS

approved

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Last modified June 27 04:02 EDT 2017. Contains 288777 sequences.