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A002301
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n!/3.
(Formerly M1861 N0737)
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10
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2, 8, 40, 240, 1680, 13440, 120960, 1209600, 13305600, 159667200, 2075673600, 29059430400, 435891456000, 6974263296000, 118562476032000, 2134124568576000, 40548366802944000, 810967336058880000
(list; graph; refs; listen; history; internal format)
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OFFSET
| 3,1
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COMMENTS
| a(n) is the number of n-permutations having 1, 2 and 3 in the same cycle. [From Geoffrey Critzer (critzer.geoffrey(AT)usd443.org), Apr 26 2009]
a(n) is the total number of 3-cycles in all n-permutations. - N. J. A. Sloane, Jul 22 2009
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REFERENCES
| N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
Letterio Toscano, Sulla Derivata di Ordinen della Funzione tg(x), Tohoku Math. J., 42 (1936), 144-154.
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LINKS
| N. J. A. Sloane, Table of n, a(n) for n = 3..30
Index to divisibility sequences
Index entries for sequences related to factorial numbers
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FORMULA
| E.g.f.: x^3/3/(1-x)
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MATHEMATICA
| f[n_]:=n!/3; Array[f, 4!, 3] [From Vladimir Orlovsky (4vladimir(AT)gmail.com), Oct 21 2009]
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PROG
| (PARI) a(n)=n!/3 \\ Charles R Greathouse IV, Jan 12 2012
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CROSSREFS
| Sequence in context: A089603 A116456 A055882 * A000828 A180736 A111394
Adjacent sequences: A002298 A002299 A002300 * A002302 A002303 A002304
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KEYWORD
| nonn,easy
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AUTHOR
| N. J. A. Sloane (njas(AT)research.att.com).
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