OFFSET
1,2
COMMENTS
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..1000
EXAMPLE
30 is a term since the harmonic mean of its divisors is 10/3 and 10*3 = 30.
138 is a term since the harmonic mean of its divisors is 23/6 and 23*6 = 138.
MATHEMATICA
q[n_] := Numerator[(hm = DivisorSigma[0, n]/DivisorSigma[-1, n])] * Denominator[hm] == n; Select[Range[10^6], q]
PROG
(PARI) isok(k) = my(d=divisors(k), h=#d/sum(i=1, #d, 1/d[i])); k == numerator(h)*denominator(h); \\ Michel Marcus, Nov 01 2021
CROSSREFS
KEYWORD
nonn
AUTHOR
Amiram Eldar, Nov 01 2021
STATUS
approved