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Search: id:A108411
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| A108411 |
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3^[n/2]. Powers of 3 repeated. |
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18
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| 1, 1, 3, 3, 9, 9, 27, 27, 81, 81, 243, 243, 729, 729, 2187, 2187, 6561, 6561, 19683, 19683, 59049, 59049, 177147, 177147, 531441, 531441, 1594323, 1594323, 4782969, 4782969, 14348907, 14348907, 43046721, 43046721, 129140163
(list; graph; listen)
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OFFSET
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0,3
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COMMENT
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a(n) is the Parker sequence for the automorphism group of the limit of the class of oriented graphs; a(n) counts the finite circulant structures in that class. - Nour-Eddine Fahssi (fahssin(AT)yahoo.fr), Feb 18 2008
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LINKS
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D. A. Gewurz and F. Merola, Sequences realized as Parker vectors of oligomorphic permutation groups, J. Integer Seq., 6 (2003), 03.1.6.
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FORMULA
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O.g.f.: -(1+x)/(-1+3*x^2). - R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Apr 01 2008
a(n)=3^(n/2)*((1+(-1)^n)/2+(1-(-1)^n)/(2*sqrt(3))). [From Paul Barry (pbarry(AT)wit.ie), Nov 12 2009]
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MAPLE
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a:=n->mul(2+(-1)^j, j=1..n):seq(a(n), n=0..27); # [From Zerinvary Lajos (zerinvarylajos(AT)yahoo.com), Dec 13 2008]
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CROSSREFS
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Essentially the same as A056449. Cf. A000244, A016116.
Sequence in context: A146474 A145957 A128019 this_sequence A056449 A162436 A146788
Adjacent sequences: A108408 A108409 A108410 this_sequence A108412 A108413 A108414
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KEYWORD
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nonn,new
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AUTHOR
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Ralf Stephan, Jun 05 2005
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