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A131561
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Period 3: repeat 1, 1, -1.
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4
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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; refs; listen; history; internal format)
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OFFSET
| 0,1
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COMMENTS
| Other than the first term, this sequence represents numerators in a fraction expansion of (ln 2)-pi/8.
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REFERENCES
| Mohammad K. Azarian, Problem 1218, Pi Mu Epsilon Journal, Vol. 13, No. 2, Spring 2010, p. 116. Solution published in Vol. 13, No. 3, Fall 2010, pp. 183-185.
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LINKS
| Index to sequences with linear recurrences with constant coefficients, signature (0,0,1).
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FORMULA
| a(n)=(1/9)*{-5*(n mod 3)+7*[(n+1) mod 3]+[(n+2) mod 3]}, with n>=0. - Paolo P. Lava (paoloplava(AT)gmail.com), 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)/((1-x)*(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]
a(n) = (-1)^[(n-1) mod 3]. - Christopher M. Richmond, Oct 07 2011
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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
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PROG
| (PARI) a(n)=1-2*(n%3==2) /* From Jaume Oliver Lafont (joliverlafont(AT)gmail.com), Mar 24 2009 */
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CROSSREFS
| Sequence in context: A162285 A071935 A096809 * A110515 A071936 A084904
Adjacent sequences: A131558 A131559 A131560 * A131562 A131563 A131564
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KEYWORD
| sign,easy
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AUTHOR
| Paul Curtz (bpcrtz(AT)free.fr), Aug 27 2007
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EXTENSIONS
| Edited by N. J. A. Sloane (njas(AT)research.att.com), Sep 15 2007
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