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A317477 Unitary harmonic numbers m such that the harmonic mean of the unitary divisors of m is also a unitary harmonic number. 1
1, 1512, 624937680, 808742880, 87348127500, 139103775360, 150780265560, 261880857000 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

The harmonic means of the unitary divisors of the terms are 1, 6, 45, 45, 45, 90, 45, 90.

LINKS

Table of n, a(n) for n=1..8.

EXAMPLE

1512 is in the sequence since the harmonic mean of its divisors is 6 and 6 is also a unitary harmonic number.

MATHEMATICA

usigma[n_] := If[n == 1, 1, Times @@ (1 + Power @@@ FactorInteger[n])]; ud[n_] := 2^PrimeNu[n]; uhQ[n_] := IntegerQ[n*ud[n]/usigma[n]]; uhuhQ[n_] :=  Module[{m = n*ud[n]/usigma[n]}, IntegerQ[m] && uhQ[m]]; Do[If[uhuhQ[n], Print[n]], {n, 1, 10^11}]

CROSSREFS

Cf. A006086, A317476.

Sequence in context: A187294 A107523 A282253 * A064584 A318713 A252508

Adjacent sequences:  A317474 A317475 A317476 * A317478 A317479 A317480

KEYWORD

nonn,more

AUTHOR

Amiram Eldar, Jul 29 2018

STATUS

approved

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Last modified January 20 19:53 EST 2022. Contains 350472 sequences. (Running on oeis4.)