A249950 Numerator of the harmonic mean of the first n cubes.

1, 16, 648, 6912, 1080000, 144000, 57624000, 526848000, 144027072000, 160030080000, 234300040128000, 255600043776000, 608349404190528000, 655145512205184000, 701941620219840000, 5989901825875968000, 31267661899936670208000, 3678548458816078848000

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: A197670 A162546 A328274 * A334734 A220298 A222916

Adjacent sequences: A249947 A249948 A249949 * A249951 A249952 A249953

Keyword

nonn

Author

Colin Barker, Nov 13 2014

Status

approved