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A128130 Expansion of (1-x)/(1+x^4); period 8: repeat [1,-1,0,0,-1,1,0,0]. 2
1, -1, 0, 0, -1, 1, 0, 0, 1, -1, 0, 0, -1, 1, 0, 0, 1, -1, 0, 0, -1, 1, 0, 0, 1, -1, 0, 0, -1, 1, 0, 0, 1, -1, 0, 0, -1, 1, 0, 0, 1, -1, 0, 0, -1, 1, 0, 0, 1, -1, 0, 0, -1, 1, 0, 0, 1, -1, 0, 0, -1, 1, 0, 0, 1, -1, 0, 0, -1, 1, 0, 0, 1, -1, 0, 0, -1, 1, 0, 0, 1, -1, 0, 0, -1, 1, 0, 0, 1, -1, 0, 0, -1, 1, 0, 0, 1, -1, 0, 0, -1, 1, 0, 0 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,1

LINKS

Antti Karttunen, Table of n, a(n) for n = 0..8191

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

FORMULA

a(n) = (sqrt(2)/4 + 1/2)*cos(3*Pi*n/4) - sqrt(2)*sin(3*Pi*n/4)/4 + (1/2 - sqrt(2)/4)*cos(Pi*n/4) - sqrt(2)*sin(Pi*n/4)/4; a(n) = Im(Sum_{k=0..n} i^(n-k+1)), i=sqrt(-1).

a(n) = (1/8)*(-(n mod 8) + ((n+2) mod 8) - 2*((n+3) mod 8) + ((n+4) mod 8) - ((n+6) mod 8) + 2*((n+7) mod 8)), with n>=0. - Paolo P. Lava, Oct 23 2007

abs(a(n)) = A133872(n). - Wesley Ivan Hurt, Feb 23 2015

a(n) = A014017(n) - A014017(n-1). - R. J. Mathar, Feb 24 2015

MAPLE

A128130 := proc(n)

    local m ;

    m := modp(n, 8) ;

    op(1+m, [1, -1, 0, 0, -1, 1, 0, 0]) ;

end proc: # R. J. Mathar, Feb 24 2015

MATHEMATICA

CoefficientList[Series[(1-x)/(1+x^4), {x, 0, 100}], x]  (* Harvey P. Dale, Mar 28 2011 *)

PROG

(Scheme) (define (A128130 n) (list-ref '(1 -1 0 0 -1 1 0 0) (modulo n 8))) ;; Antti Karttunen, Aug 12 2017

CROSSREFS

Cf. A014017, A133872.

Sequence in context: A073784 A320006 A219977 * A133872 A286903 A339052

Adjacent sequences:  A128127 A128128 A128129 * A128131 A128132 A128133

KEYWORD

easy,sign

AUTHOR

Paul Barry, Feb 15 2007

EXTENSIONS

More terms from Antti Karttunen, Aug 12 2017

STATUS

approved

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Last modified December 7 20:40 EST 2021. Contains 349589 sequences. (Running on oeis4.)