Triple factorial numbers a(n) = n!!!, defined by a(n) = n*a(n-3), a(0) = a(1) = 1, a(2) = 2. (Formerly M0596) +0 24 1, 1, 2, 3, 4, 10, 18, 28, 80, 162, 280, 880, 1944, 3640, 12320, 29160, 58240, 209440, 524880, 1106560, 4188800, 11022480, 24344320, 96342400, 264539520, 608608000, 2504902400, 7142567040, 17041024000, 72642169600 (list; graph; listen) OFFSET 0,3 REFERENCES J. Spanier and K. B. Oldham, An Atlas of Functions, Hemisphere, NY, 1987, p. 23. LINKS T. D. Noe, Table of n, a(n) for n=0..200 M. L. Perez, Smarandache k-factorials Eric Weisstein's World of Mathematics, Link to a section of The World of Mathematics. FORMULA a(n) = product( n-3i, i=0..[(n-1)/3] ) - M. F. Hasler (Maximilian.Hasler(AT)gmail.com), Feb 16 2008 PROGRAM (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 CROSSREFS Cf. A000142, A006882 (= A001147 union A000165), A007662. Sequence in context: A055506 A098088 A080500 this_sequence A049891 A135432 A108364 Adjacent sequences: A007658 A007659 A007660 this_sequence A007662 A007663 A007664 KEYWORD nonn,easy,nice AUTHOR njas, Mira Bernstein, Robert G. Wilson v (rgwv(AT)rgwv.com) page 1 Search completed in 0.002 seconds