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 A249950 Numerator of the harmonic mean of the first n cubes. 2
 1, 16, 648, 6912, 1080000, 144000, 57624000, 526848000, 144027072000, 160030080000, 234300040128000, 255600043776000, 608349404190528000, 655145512205184000, 701941620219840000, 5989901825875968000, 31267661899936670208000, 3678548458816078848000 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS A007408 contains the corresponding denominators. LINKS Colin Barker, Table of n, a(n) for n = 1..750 EXAMPLE a(3) = 648 because the first 3 cubes are [1,8,27] and 3 / (1/1+1/8+1/27) = 648/251. MATHEMATICA Table[Numerator[n/Sum[1/k^3, {k, 1, n}]], {n, 1, 20}] (* Vaclav Kotesovec, Nov 14 2014 *) Table[Numerator[HarmonicMean[Range[n]^3]], {n, 20}] (* Harvey P. Dale, Aug 20 2017 *) PROG (PARI) harmonicmean(v) = #v / sum(k=1, #v, 1/v[k]) s=vector(30); for(k=1, #s, s[k]=numerator(harmonicmean(vector(k, i, i^3)))); s CROSSREFS Cf. A007408. Sequence in context: A128048 A197670 A162546 * A220298 A222916 A197407 Adjacent sequences:  A249947 A249948 A249949 * A249951 A249952 A249953 KEYWORD nonn AUTHOR Colin Barker, Nov 13 2014 STATUS approved

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Last modified December 16 09:34 EST 2018. Contains 318160 sequences. (Running on oeis4.)