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A108411 a(n) = 3^floor(n/2). Powers of 3 repeated. 32
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; refs; listen; history; text; internal format)
OFFSET

0,3

COMMENTS

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

LINKS

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).

FORMULA

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

EXAMPLE

a(6) = 27; 3^floor(6/2) = 3^floor(3) = 3^3 = 27.

MAPLE

A108411:=n->3^floor(n/2); seq(A108411(k), k=0..100); # Wesley Ivan Hurt, Nov 01 2013

MATHEMATICA

Table[3^Floor[n/2], {n, 0, 100}] (* Wesley Ivan Hurt, Nov 01 2013 *)

PROG

(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

CROSSREFS

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

KEYWORD

nonn,easy

AUTHOR

Ralf Stephan, Jun 05 2005

STATUS

approved

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Last modified December 11 05:22 EST 2019. Contains 329913 sequences. (Running on oeis4.)