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A109007 GCD(n,3). +0
7
3, 1, 1, 3, 1, 1, 3, 1, 1, 3, 1, 1, 3, 1, 1, 3, 1, 1, 3, 1, 1, 3, 1, 1, 3, 1, 1, 3, 1, 1, 3, 1, 1, 3, 1, 1, 3, 1, 1, 3, 1, 1, 3, 1, 1, 3, 1, 1, 3, 1, 1, 3, 1, 1, 3, 1, 1, 3, 1, 1, 3, 1, 1, 3, 1, 1, 3, 1, 1, 3, 1, 1, 3, 1, 1, 3, 1, 1, 3, 1, 1, 3, 1, 1, 3, 1, 1, 3, 1, 1, 3, 1, 1, 3, 1, 1, 3, 1, 1, 3, 1 (list; graph; listen)
OFFSET

0,1

COMMENT

For n>1: a(n) = GCD of the n-th and (n+2)-th triangular numbers = A050873(A000217(n+2),A000217(n)). - Reinhard Zumkeller (reinhard.zumkeller(AT)gmail.com), May 28 2007

FORMULA

a(n) = 1 + 2*[3|n] = 1 + 2(1 + 2*cos(2*n*Pi/3])/3, where [x|y] = 1 when x divides y, 0 otherwise.

a(n) = a(n-3).

Multiplicative with a(p^e, 3) = GCD(p^e, 3). David W. Wilson (davidwwilson(AT)comcast.net) Jun 12, 2005.

O.g.f.: -(3+x+x^2)/((x-1)*(x^2+x+1)) . - R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Nov 24 2007

CROSSREFS

Cf. A109004.

Cf. A026741, A130334.

Sequence in context: A098094 A087283 A111625 this_sequence A132951 A101685 A049653

Adjacent sequences: A109004 A109005 A109006 this_sequence A109008 A109009 A109010

KEYWORD

nonn,easy,mult

AUTHOR

Mitch Harris (Harris.Mitchell(AT)mgh.harvard.edu)

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Last modified July 26 23:19 EDT 2008. Contains 142293 sequences.


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