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Search: id:A006231
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| A006231 |
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Sum_{k=2..n} n(n-1)...(n-k+1)/k.
(Formerly M3908)
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+0
7
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| 0, 1, 5, 20, 84, 409, 2365, 16064, 125664, 1112073, 10976173, 119481284, 1421542628, 18348340113, 255323504917, 3809950976992, 60683990530208, 1027542662934897, 18430998766219317, 349096664728623316
(list; graph; listen)
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OFFSET
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1,3
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COMMENT
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a(n) is also the number of permutations in the symmetric group S_n that are pure cycles - Avi Peretz (njk(AT)netvision.net.il), Mar 24 2001
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REFERENCES
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N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
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LINKS
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T. D. Noe, Table of n, a(n) for n=1..100
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EXAMPLE
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a(3) = 5 because the cycles in S_3 are (12), (13), (23), (123), (132).
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CROSSREFS
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Differences satisfy a(n+1)-a(n)=A000522(n)-1.
Cf. A059760.
Sequence in context: A006749 A002213 A099949 this_sequence A069007 A126987 A152185
Adjacent sequences: A006228 A006229 A006230 this_sequence A006232 A006233 A006234
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KEYWORD
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nonn,easy,nice
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AUTHOR
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R. K. Guy
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EXTENSIONS
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More terms from Larry Reeves (larryr(AT)acm.org), Mar 27 2001
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