A382351 Numbers with an integer harmonic mean of the indices of distinct prime factors.

2, 3, 4, 5, 7, 8, 9, 11, 13, 16, 17, 19, 23, 25, 27, 29, 31, 32, 37, 39, 41, 43, 47, 49, 53, 59, 61, 64, 65, 67, 71, 73, 79, 81, 83, 89, 97, 101, 103, 107, 109, 113, 117, 121, 125, 127, 128, 130, 131, 137, 139, 149, 151, 157, 163, 167, 169, 173, 179, 181, 191, 193, 195, 197, 199, 211

Offset: 1

Author

Ilya Gutkovskiy, Mar 22 2025

Keywords

• nonn

Links

• Index entries for sequences computed from indices in prime factorization.

Crossrefs

Cf. A067340, A078174, A326621.

Programs

Mathematica

Select[Range[2, 220], IntegerQ[HarmonicMean[PrimePi[#[[1]]] & /@ FactorInteger[#]]] &]

PARI

isok(k) = if (k>1, my(f=factor(k)); denominator(#f~/sum(i=1, #f~, 1/primepi(f[i,1]))) == 1); \\ Michel Marcus, Mar 22 2025