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A108411
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a(n) = 3^floor(n/2). Powers of 3 repeated.
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32
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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
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OFFSET
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0,3
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COMMENTS
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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. - N-E. Fahssi, Feb 18 2008
Complete sequence: every positive integer is the sum of members of this sequence. - Charles R Greathouse IV, Jul 19 2012
a(n+1) = sum of row n in triangle A152842. - Reinhard Zumkeller, May 01 2014
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LINKS
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Vincenzo Librandi, Table of n, a(n) for n = 0..3000
D. A. Gewurz and F. Merola, Sequences realized as Parker vectors of oligomorphic permutation groups, J. Integer Seq., 6 (2003), 03.1.6.
Index entries for linear recurrences with constant coefficients, signature (0,3).
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FORMULA
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O.g.f.: (1+x)/(1-3*x^2). - R. J. Mathar, Apr 01 2008
a(n) = 3^(n/2)*((1+(-1)^n)/2+(1-(-1)^n)/(2*sqrt(3))). - Paul Barry, Nov 12 2009
a(n+3) = a(n+2)*a(n+1)/a(n). - Reinhard Zumkeller, Mar 04 2011
a(n) = (-1)^n*sum(A158020(n,k)*2^k, 0<=k<=n). - Philippe Deléham, Dec 01 2011
a(n) = sum(A152815(n,k)*2^k, 0<=k<=n). - Philippe Deléham, Apr 22 2013
a(n) = 3^A004526(n). - Michel Marcus, Aug 30 2014
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EXAMPLE
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a(6) = 27; 3^floor(6/2) = 3^floor(3) = 3^3 = 27.
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MAPLE
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A108411:=n->3^floor(n/2); seq(A108411(k), k=0..100); # Wesley Ivan Hurt, Nov 01 2013
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MATHEMATICA
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Table[3^Floor[n/2], {n, 0, 100}] (* Wesley Ivan Hurt, Nov 01 2013 *)
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PROG
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(PARI) a(n)=3^floor(n/2);
(MAGMA) [3^Floor(n/2): n in [0..50]]; // Vincenzo Librandi, Aug 17 2011
(Haskell)
a108411 = (3 ^) . flip div 2 -- Reinhard Zumkeller, May 01 2014
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CROSSREFS
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Essentially the same as A056449 and A162436.
Cf. A000244, A016116.
Sequence in context: A145957 A214439 A128019 * A056449 A287479 A162436
Adjacent sequences: A108408 A108409 A108410 * A108412 A108413 A108414
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KEYWORD
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nonn,easy
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AUTHOR
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Ralf Stephan, Jun 05 2005
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STATUS
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approved
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