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A027611
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Denominator of n * n-th harmonic number.
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22
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1, 1, 2, 3, 12, 10, 20, 35, 280, 252, 2520, 2310, 27720, 25740, 24024, 45045, 720720, 680680, 4084080, 3879876, 739024, 235144, 5173168, 14872858, 356948592, 343219800, 2974571600, 2868336900, 80313433200, 77636318760
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OFFSET
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1,3
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COMMENTS
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This is very similar to A128438, which is a different sequence. They differ at n=6 (and nowhere else?). - N. J. A. Sloane, Nov 21 2008
Denominator of 1/n + 2/(n-1) + 3/(n-2) + ... + (n-1)/2 + n.
Denominator of Sum_{k=1..n} frac(n/k) where frac(x/y) denotes the fractional part of x/y. - Benoit Cloitre, Oct 03 2002
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LINKS
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FORMULA
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a(n) = denominators of coefficients in expansion of -log(1-x)/(1-x)^2.
a(n) = denominators of (n+1)*(harmonic(n+1) - 1).
a(n) = denominators of (n+1)*(Psi(n+2) + Euler-gamma - 1). (End)
a(n) = numerator(h(n)/h(n-1)) - denominator(h(n)/h(n-1)), n > 1, where h(n) is the n-th harmonic number. - Gary Detlefs, Sep 03 2011
a(n) = denominators of coefficients of e.g.f. -1 + exp(x)*(1 + Sum_{j >= 0} (-x)^(j+1)/(j * j!)). - G. C. Greubel, Aug 24 2022
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MAPLE
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a := n -> denom(add((n-j)/j, j=1..n));
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MATHEMATICA
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PROG
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(Haskell)
import Data.Ratio ((%), denominator)
a027611 n = denominator $ sum $ map (n %) [1..n]
(Magma) [Denominator(n*HarmonicNumber(n)): n in [1..40]]; // Vincenzo Librandi, Feb 19 2014
(PARI) a(n) = denominator(n*sum(k=1, n, 1/k)); \\ Michel Marcus, Feb 15 2015
(Python)
from sympy import harmonic
(SageMath) [denominator(n*harmonic_number(n)) for n in (1..40)] # G. C. Greubel, Aug 24 2022
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CROSSREFS
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KEYWORD
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nonn,easy,frac
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AUTHOR
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Glen Burch (gburch(AT)erols.com)
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EXTENSIONS
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STATUS
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approved
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