OFFSET
1,2
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..500
EXAMPLE
The harmonic mean of the divisors of 468 is 324/49 = (18/7)^2, the square of a rational number, so 468 is a term of the sequence.
MATHEMATICA
H[l_] := Module[{m, s}, m = Length[l]; s = 0; For[i = 1, i <= m, i++, s = s + (1/l[[i]])]; s = s/m; s = 1/s; s] r = {}; Do[d = Divisors[n]; h = H[d]; num = Numerator[h]; den = Denominator[h]; If[IntegerQ[num^(1/2)] && IntegerQ[den^(1/2)], r = Append[r, n]], {n, 1, 10^6}]; r
CROSSREFS
KEYWORD
nonn
AUTHOR
Joseph L. Pe, Sep 20 2002
STATUS
approved