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Search: id:A034001
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| A034001 |
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One third of triple factorial numbers. |
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+0
11
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| 1, 6, 54, 648, 9720, 174960, 3674160, 88179840, 2380855680, 71425670400, 2357047123200, 84853696435200, 3309294160972800, 138990354760857600, 6254565964238592000, 300219166283452416000, 15311177480456073216000
(list; graph; listen)
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OFFSET
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1,2
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LINKS
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INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 495
N. J. A. Sloane and Thomas Wieder, The Number of Hierarchical Orderings, Order 21 (2004), 83-89.
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FORMULA
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3*a(n) = (3*n)!!! := product(3*j, j=1..n) = 3^n*n!; E.g.f. (-1+1/(1-3*x))/3.
E.g.f. : 1/(1-3x)^2 - Paul Barry (pbarry(AT)wit.ie), Sep 14 2004
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MAPLE
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with(combstruct); SeqSeqSeqL := [T, {T=Sequence(S), S=Sequence(U, card >= 1), U=Sequence(Z, card > =1)}, labeled]; seq(count(SeqSeqSeqL, size=j), j=1..12);
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CROSSREFS
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Cf. A007559, A034000.
Sequence in context: A109576 A069726 A081132 this_sequence A084062 A137591 A072034
Adjacent sequences: A033998 A033999 A034000 this_sequence A034002 A034003 A034004
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KEYWORD
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easy,nonn
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AUTHOR
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Wolfdieter Lang (wolfdieter.lang(AT)physik.uni-karlsruhe.de)
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