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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
OFFSET
1,2
COMMENTS
The harmonic means of the unitary divisors of the terms are 1, 6, 45, 45, 45, 90, 45, 90.
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
Sequence in context: A107523 A282253 A368545 * A064584 A318713 A252508
KEYWORD
nonn,more
AUTHOR
Amiram Eldar, Jul 29 2018
STATUS
approved