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A128016
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Expansion of (1+x+x^2+x^3)/(1-x^2+x^4).
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1
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1, 1, 2, 2, 1, 1, -1, -1, -2, -2, -1, -1, 1, 1, 2, 2, 1, 1, -1, -1, -2, -2, -1, -1, 1, 1, 2, 2, 1, 1, -1, -1, -2, -2, -1, -1, 1, 1, 2, 2, 1, 1, -1, -1, -2, -2, -1, -1, 1, 1, 2, 2, 1, 1, -1, -1, -2, -2, -1, -1, 1, 1, 2, 2, 1, 1, -1, -1, -2, -2, -1, -1
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,3
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COMMENTS
| Periodic{1,1,2,2,1,1,-1,-1,-2,-2,-1,-1}.
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FORMULA
| G.f.: (1-x^4)/(1-x-x^2+x^3+x^4-x^5); a(n)=cos(5*pi*n/6)/2+(1-sqrt(3)/2)sin(5*pi*n/6)+cos(pi*n/6)/2+(1+sqrt(3)/2)sin(pi*n/6);
a(n)=(1/12)*{-2*[n mod 12]-[(n+2) mod 12]+[(n+4) mod 12]+2*[(n+6) mod 12]+[(n+8) mod 12]-[(n+10) mod 12]}, with n>=0. - Paolo P. Lava (paoloplava(AT)gmail.com), Jun 01 2007
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CROSSREFS
| Cf. A128017.
Sequence in context: A138385 A030614 * A128017 A096285 A175078 A121561
Adjacent sequences: A128013 A128014 A128015 * A128017 A128018 A128019
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KEYWORD
| easy,sign
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AUTHOR
| Paul Barry (pbarry(AT)wit.ie), Feb 11 2007
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