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 A004080 Least k such that H(k) >= n, where H(k) is the harmonic number sum_{i=1..k} 1/i. 29
 0, 1, 4, 11, 31, 83, 227, 616, 1674, 4550, 12367, 33617, 91380, 248397, 675214, 1835421, 4989191, 13562027, 36865412, 100210581, 272400600, 740461601, 2012783315, 5471312310, 14872568831, 40427833596, 109894245429, 298723530401, 812014744422 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 REFERENCES Bruno Rizzi and Cristina Scagliarini: I numeri armonici. Periodico di matematiche, "Mathesis", pp. 17-58, 1986, numbers 1-2 [From Vincenzo Librandi, Jan 05 2009] W. Sierpiński, Sur les decompositions de nombres rationnels, Oeuvres Choisies, Académie Polonaise des Sciences, Warsaw, Poland, 1974, p. 181. N. J. A. Sloane, Illustration for sequence M4299 (=A007340) in The Encyclopedia of Integer Sequences (with Simon Plouffe), Academic Press, 1995. LINKS T. D. Noe, Table of n, a(n) for n=0..100 (using Hickerson's formula in A002387) John V. Baxley, Euler's constant, Taylor's formula, and slowly converging series, Math. Mag. 65 (1992), 302-313. R. P. Boas, Jr. and J. W. Wrench, Jr., Partial sums of the harmonic series, Amer. Math. Monthly, 78 (1971), 864-870. Keneth Adrian Dagal, A Lower Bound for tau(n) for k-Multiperfect Number, arXiv:1309.3527 [math.NT] J. Sondow and E. W. Weisstein, MathWorld: Harmonic Number Eric Weisstein's World of Mathematics, Harmonic Series Eric Weisstein's World of Mathematics, High-Water Mark FORMULA The quotient of two successive terms of this sequence has exp(1) for limit. - Sébastien Dumortier, Jun 29 2005 a(n) = exp(n - gamma + o(1)). - Charles R Greathouse IV, Mar 10 2009 a(n) = A002387(n) for n>1. - Robert G. Wilson v, Jun 18 2015 EXAMPLE a(2)=4 because 1/1 + 1/2 + 1/3 + 1/4 > 2. MAPLE ListA004080:=proc(q) local a, k, n; a:=1; print(a); k:=1; for n from 2 to q do while a aux[n - 1], Print[n]], {n, 1, 14000}] (* José María Grau Ribas, Feb 20 2010 *) a[0] = 0; a[1] = 1; a[n_] := k /. FindRoot[ HarmonicNumber[k] == n, {k, Exp[n - EulerGamma]}, WorkingPrecision -> 50] // Ceiling; Table[a[n], {n, 0, 28}] (* Jean-François Alcover, Aug 13 2013, after Charles R Greathouse IV *) PROG (PARI) gp > t=0; n=0; for(i=1, 10^20, t+=1./i; if(t>=n, print(i, " ", t); n++)) \\ Thomas Gettys (tpgettys(AT)comcast.net), Jan 21 2007 (Haskell) import Data.List (findIndex); import Data.Maybe (fromJust) a004080 n = fromJust \$    findIndex (fromIntegral n <=) \$ scanl (+) 0 \$ map recip [1..] -- Reinhard Zumkeller, Jul 13 2014 CROSSREFS Apart from first two terms, same as A002387. Sequence in context: A104743 A165993 A192312 * A298300 A027115 A077995 Adjacent sequences:  A004077 A004078 A004079 * A004081 A004082 A004083 KEYWORD nonn,nice AUTHOR EXTENSIONS Terms for n >= 13 computed by Eric W. Weisstein; corrected by James R. Buddenhagen and Eric W. Weisstein, Feb 18 2001 Edited by Dean Hickerson, Apr 19 2003 More terms from Sébastien Dumortier, Jun 29 2005 a(27) from Thomas Gettys (tpgettys(AT)comcast.net), Dec 05 2006 a(28) from Thomas Gettys (tpgettys(AT)comcast.net), Jan 21 2007 Edited by Charles R Greathouse IV, Mar 24 2010 STATUS approved

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Last modified December 10 04:15 EST 2019. Contains 329885 sequences. (Running on oeis4.)