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A096620
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Denominator of -3n + 2(1+n)*HarmonicNumber(n).
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6
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1, 1, 1, 3, 6, 5, 10, 35, 140, 126, 1260, 1155, 13860, 12870, 12012, 45045, 360360, 340340, 2042040, 1939938, 369512, 117572, 2586584, 7436429, 178474296, 171609900, 1487285800, 1434168450, 40156716600, 38818159380
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,4
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COMMENTS
| Also, with initial term 0 (really this is A093419), denominator of q_n = -4n + 2(1+n)*HarmonicNumber[n] (Cameron). Cf. A115107.
Average time to quicksort n items in random order
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REFERENCES
| P. J. Cameron, Combinatorics, Cambridge Univ. Press, 1996, see p. 68.
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LINKS
| Eric Weisstein's World of Mathematics, Quicksort
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FORMULA
| a(n) = Denominator(2*(n+1)*HarmonicNumber(n+1)-1). [From Gary Detlefs, Sep 14 2011]
a(n)=Denominator((H(n+1)+H(n))/(H(n+1)-H(n))), where H(n) is the n-th harmonic number. [From Gary Detlefs, Oct 03 2011]
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EXAMPLE
| 0, 1, 3, 17/3, 53/6, 62/5, 163/10, 717/35, 3489/140, ...
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CROSSREFS
| Cf. A093418, A115107.
Sequence in context: A123089 A127780 A118413 * A093419 A160049 A007479
Adjacent sequences: A096617 A096618 A096619 * A096621 A096622 A096623
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KEYWORD
| nonn,frac
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AUTHOR
| Eric Weisstein (eric(AT)weisstein.com), Jul 01, 2004
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EXTENSIONS
| Offset corrected by Gary Detlefs Sep 14 2011
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