%I A007661 M0596
%S A007661 1,1,2,3,4,10,18,28,80,162,280,880,1944,3640,12320,29160,
%T A007661 58240,209440,524880,1106560,4188800,11022480,24344320,96342400,
%U A007661 264539520,608608000,2504902400,7142567040,17041024000,72642169600
%N A007661 Triple factorial numbers a(n) = n!!!, defined by a(n) = n*a(n-3), a(0) 
               = a(1) = 1, a(2) = 2.
%D A007661 N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, 
               Academic Press, 1995 (includes this sequence).
%D A007661 J. Spanier and K. B. Oldham, An Atlas of Functions, Hemisphere, NY, 1987, 
               p. 23.
%H A007661 T. D. Noe, <a href="b007661.txt">Table of n, a(n) for n=0..200</a>
%H A007661 M. L. Perez, <a href="http://www.gallup.unm.edu/~smarandache/SKF.htm">
               Smarandache k-factorials</a>
%H A007661 Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/
               Multifactorial.html">Link to a section of The World of Mathematics.</
               a>
%F A007661 a(n) = product( n-3i, i=0..[(n-1)/3] ) - M. F. Hasler (Maximilian.Hasler(AT)gmail.com), 
               Feb 16 2008
%o A007661 (PARI) a(n,d=3)=prod(i=0,(n-1)\d,n-d*i) - M. F. Hasler (Maximilian.Hasler(AT)gmail.com), 
               Feb 16 2008
%Y A007661 Cf. A000142, A006882 (= A001147 union A000165), A007662.
%Y A007661 Sequence in context: A055506 A098088 A080500 this_sequence A049891 A135432 
               A108364
%Y A007661 Adjacent sequences: A007658 A007659 A007660 this_sequence A007662 A007663 
               A007664
%K A007661 nonn,easy,nice
%O A007661 0,3
%A A007661 N. J. A. Sloane (njas(AT)research.att.com), Mira Bernstein, Robert G. 
               Wilson v (rgwv(AT)rgwv.com)