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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
OFFSET
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).
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
Sequence in context: A073784 A320006 A219977 * A133872 A286903 A339052
KEYWORD
easy,sign
AUTHOR
Paul Barry, Feb 15 2007
EXTENSIONS
More terms from Antti Karttunen, Aug 12 2017
STATUS
approved