OFFSET
1,1
COMMENTS
Includes all the squares of primes (A001248), since they are the numbers with a single noninfinitary divisor.
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..5000
EXAMPLE
12 is a term since its noninfinitary divisors are {2, 6}, and their harmonic mean, 3, is an integer.
MATHEMATICA
nidiv[1] = {}; nidiv[n_] := Complement[Divisors[n], Sort@ Flatten@ Outer[Times, Sequence @@ (FactorInteger[n] /. {p_, m_Integer} :> p^Select[Range[0, m], BitOr[m, #] == m &])]]; Select[Range[5000], (d = nidiv[#]) != {} && IntegerQ@ HarmonicMean[d] &]
CROSSREFS
KEYWORD
nonn
AUTHOR
Amiram Eldar, Nov 04 2021
STATUS
approved