%I A108411
%S A108411 1,1,3,3,9,9,27,27,81,81,243,243,729,729,2187,2187,6561,6561,19683,
%T A108411 19683,59049,59049,177147,177147,531441,531441,1594323,1594323,4782969,
%U A108411 4782969,14348907,14348907,43046721,43046721,129140163
%N A108411 3^[n/2]. Powers of 3 repeated.
%C A108411 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
%H A108411 D. A. Gewurz and F. Merola, <a href="http://www.cs.uwaterloo.ca/journals/
               JIS/VOL6/Gewurz/gewurz5.html">Sequences realized as Parker vectors 
               of oligomorphic permutation groups</a>, J. Integer Seq., 6 (2003), 
               03.1.6.
%F A108411 O.g.f.: -(1+x)/(-1+3*x^2). - R. J. Mathar (mathar(AT)strw.leidenuniv.nl), 
               Apr 01 2008
%F A108411 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]
%p A108411 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]
%Y A108411 Essentially the same as A056449. Cf. A000244, A016116.
%Y A108411 Sequence in context: A146474 A145957 A128019 this_sequence A056449 A162436 
               A146788
%Y A108411 Adjacent sequences: A108408 A108409 A108410 this_sequence A108412 A108413 
               A108414
%K A108411 nonn,new
%O A108411 0,3
%A A108411 Ralf Stephan, Jun 05 2005