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A006595
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(n+2)!/4 + n!/2.
(Formerly M1794)
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1
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1, 2, 7, 33, 192, 1320, 10440, 93240, 927360, 10160640, 121564800, 1576713600, 22034073600, 330032102400, 5274286617600, 89575694208000, 1611054821376000, 30589118816256000, 611426688897024000
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,2
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REFERENCES
| L. Comtet, Advanced Combinatorics, Reidel, 1974, p. 258.
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
J. R. Stembridge, Some combinatorial aspects of reduced words in finite Coxeter groups. Trans. Amer. Math. Soc. 349 (1997), no. 4, 1285-1332.
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CROSSREFS
| A diagonal of A059418.
Sequence in context: A104981 A121965 A058797 * A179525 A059099 A020103
Adjacent sequences: A006592 A006593 A006594 * A006596 A006597 A006598
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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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EXTENSIONS
| Improved description and sequence extended, 8/95.
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