A348694 a(n) is the least number k such that the numerator of the harmonic mean of the divisors of k is equal to n, or -1 if no such k exists.

1, 6, 3, 2, 5, 270, 7, 672, 84, 30, 11, 4, 13, 18620, 420, 24, 17, 12, 19, 10, 21, 22, 23, 30240, 1550, 78, 9, 168, 29, 60, 31, 8, 132, 102, 35, 18, 37, 38, 39, 3360, 41, 3724, 43, 7392, 45, 15456, 47, 1080, 49, 6051500, 153, 26, 53, 540, 55, 56, 57, 174, 59, 90

Offset: 1

Author

Amiram Eldar, Oct 30 2021

Keywords

• nonn

Examples

			a(2) = 6 since the harmonic mean of the divisors of 6 is 2.
a(3) = 3 since the harmonic mean of the divisors of 3 is 3/2.
		

Links

• Amiram Eldar, Table of n, a(n) for n = 1..179
• Amiram Eldar, Table of n, a(n) for n = 1..1000 with 9 holes marked with 0

Crossrefs

Cf. A099377, A099378, A348695.

Programs

Mathematica

num[n_] := Numerator[DivisorSigma[0, n]/DivisorSigma[-1, n]]; seq[m_] := Module[{s = Table[0, {m}], c = 0, n = 1, i}, While[c < m, i = num[n]; If[i <= m && s[[i]] == 0, c++; s[[i]] = n]; n++]; s]; seq[100]