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A099838 Expansion of (1-x)^2(1+x)/(1+x+x^2). 6
1, -2, 0, 3, -3, 0, 3, -3, 0, 3, -3, 0, 3, -3, 0, 3, -3, 0, 3, -3, 0, 3, -3, 0, 3, -3, 0, 3, -3, 0, 3, -3, 0, 3, -3, 0, 3, -3, 0, 3, -3, 0, 3, -3, 0, 3, -3, 0, 3, -3, 0, 3, -3, 0, 3, -3, 0, 3, -3, 0, 3, -3, 0, 3, -3, 0, 3, -3, 0, 3, -3, 0, 3, -3, 0, 3, -3, 0, 3, -3, 0, 3, -3, 0, 3, -3, 0, 3, -3, 0, 3, -3, 0, 3, -3, 0, 3, -3, 0, 3, -3, 0 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

COMMENTS

Partial sums are A099837.

LINKS

Table of n, a(n) for n=0..101.

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

FORMULA

a(n)=sum{k=0..n, (cos(2*pi*(n-k)/3)+sin(2*pi*(n-k)/3)/sqrt(3))C(2, k)(-1)^k}

for n>=2 : a(n)=2*sqrt(3)*cos((4*n+1)*Pi/6) [From Richard Choulet, Apr 23 2009]

CROSSREFS

Sequence in context: A258817 A004557 A088276 * A127449 A138057 A053727

Adjacent sequences:  A099835 A099836 A099837 * A099839 A099840 A099841

KEYWORD

easy,sign

AUTHOR

Paul Barry, Oct 27 2004

STATUS

approved

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Last modified July 17 02:52 EDT 2019. Contains 325092 sequences. (Running on oeis4.)