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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 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.)