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A131561 Period 3: repeat 1, 1, -1. +0
2
1, 1, -1, 1, 1, -1, 1, 1, -1, 1, 1, -1, 1, 1, -1, 1, 1, -1, 1, 1, -1, 1, 1, -1, 1, 1, -1, 1, 1, -1, 1, 1, -1, 1, 1, -1, 1, 1, -1, 1, 1, -1, 1, 1, -1, 1, 1, -1, 1, 1, -1, 1, 1, -1, 1, 1, -1, 1, 1, -1, 1, 1, -1, 1, 1, -1, 1, 1, -1, 1, 1, -1, 1, 1, -1, 1, 1, -1, 1, 1, -1, 1, 1, -1, 1, 1, -1, 1, 1, -1, 1, 1, -1, 1, 1, -1, 1, 1, -1, 1, 1, -1, 1, 1, -1, 1, 1, -1, 1, 1 (list; graph; listen)
OFFSET

0,1

FORMULA

a(n)=(1/9)*{-5*(n mod 3)+7*[(n+1) mod 3]+[(n+2) mod 3]}, with n>=0. - Paolo P. Lava (ppl(AT)spl.at), Aug 28 2007

a(n) = (4*cos((2*n - 1) * Pi/3) + 1) / 3 - Federico Acha Neckar (f0383864(AT)hotmail.com), Sep 02 2007

G.f.: (-1-x+x^2)/(x-1)/(x^2+x+1). - R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Nov 14 2007

G.f.: (1+x-x^2)/(1-x^3) [From Jaume Oliver Lafont (joliverlafont(AT)gmail.com), Mar 24 2009]

MAPLE

A131561 := proc(n) op((n mod 3)+1, [1, 1, -1]) ; end: seq(A131561(n), n=0..120) ; - R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Oct 18 2007

PROGRAM

(PARI) a(n)=1-2*(n%3==2) [From Jaume Oliver Lafont (joliverlafont(AT)gmail.com), Mar 24 2009]

CROSSREFS

Sequence in context: A065357 A071935 A096809 this_sequence A110515 A071936 A084904

Adjacent sequences: A131558 A131559 A131560 this_sequence A131562 A131563 A131564

KEYWORD

sign,easy

AUTHOR

Paul Curtz (bpcrtz(AT)free.fr), Aug 27 2007

EXTENSIONS

Edited by N. J. A. Sloane (njas(AT)research.att.com), Sep 15 2007

More terms from R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Oct 18 2007

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Last modified November 25 20:09 EST 2009. Contains 167514 sequences.


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