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This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.

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A317476 Harmonic numbers k such that the harmonic mean of the divisors of k is also a harmonic number.

Original entry on oeis.org

1, 270, 164989440, 2701389600, 71271827200, 183694492800, 7322605472000, 28103080287744
Offset: 1

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Author

Amiram Eldar, Jul 29 2018

Keywords

Comments

The harmonic means of the divisors of the terms are 1, 6, 140, 270, 270, 672, 672, 496.
The terms 1, 2701389600 and 71271827200 have harmonic means of divisors which are also in this sequence.

Examples

			270 is in the sequence since the harmonic mean of its divisors is 6, which is also a harmonic number.

Crossrefs

Cf. A001599, A317477.

Programs

  • Mathematica
    hQ[n_] := IntegerQ[n*DivisorSigma[0, n]/DivisorSigma[1, n]]; hhQ[n_] :=  Module[{h = n * DivisorSigma[0, n]/DivisorSigma[1, n]}, IntegerQ[h] && hQ[h]]; Do[If[hhQ[n], Print[n]], {n, 1, 10^14}]
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Started in 1964 by Neil J. A. Sloane | Maintained by The OEIS Foundation Inc.

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