%I A011781
%S A011781 1,3,27,405,8505,229635,7577955,295540245,13299311025,678264862275,
%T A011781 38661097149675,2435649120429525,168059789309637225,
%U A011781 12604484198222791875,1020963220056046141875,88823800144876014343125
%N A011781 Sextuple factorial numbers: product[ k=0..n-1 ] (6*k+3).
%C A011781 Total number of Eulerian circuits in rooted labeled multigraphs with 
               n edges. - Valery A. Liskovets (liskov(AT)im.bas-net.by), Apr 07 
               2002
%D A011781 V. A. Liskovets, A note on the total number of Eulerian circuits in multigraphs. 
               In press.
%D A011781 B.Lass, D'emonstration combinatoire de la formule de Harer-Zagier, C. 
               R. Acad. Sci. Paris, Serie I, 333 (2001) No 3, 155-160.
%H A011781 Valery Liskovets, <a href="http://www.cs.uwaterloo.ca/journals/JIS/index.html">
               A Note on the Total Number of Double Eulerian Circuits in Multigraphs 
               </a>, Journal of Integer Sequences, Vol. 5 (2002), Article 02.2.5
%F A011781 E.g.f. (1-6*x)^(-1/2).
%F A011781 a(n) = 3^n*(2*n-1)!!.
%t A011781 s=1;lst={s};Do[s+=n*s;AppendTo[lst, s], {n, 2, 5!, 6}];lst [From Vladimir 
               Orlovsky (4vladimir(AT)gmail.com), Nov 08 2008]
%o A011781 (PARI) a(n)=if(n<0,0,(3/2)^n*(2*n)!/n!)
%Y A011781 Cf. A001147, A047657, A049308.
%Y A011781 Cf. A069736.
%Y A011781 Sequence in context: A157089 A138436 A141057 this_sequence A094577 A108525 
               A136719
%Y A011781 Adjacent sequences: A011778 A011779 A011780 this_sequence A011782 A011783 
               A011784
%K A011781 nonn
%O A011781 0,2
%A A011781 killough(AT)wagner.convex.com (Lee D. Killough)