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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.)