A348695 a(n) is the least number k such that the denominator of the harmonic mean of the divisors of k is equal to n, or -1 if no such k exists.

1, 3, 2, 7, 24, 11, 4, 21, 10, 19, 258, 23, 9, 39, 8, 31, 402, 55, 37, 57, 26, 43, 3836, 47, 216, 99, 34, 124, 4844, 59, 16, 93, 86, 67, 76, 71, 73, 111, 125, 79, 978, 83, 7196, 129, 58, 411, 7868, 155, 52, 447, 101, 63, 1266, 107, 109, 372, 74, 519, 9884, 203

Offset

1,2

Links

Amiram Eldar, Table of n, a(n) for n = 1..1000

Example

a(2) = 3 since the harmonic mean of the divisors of 3 is 3/2.
a(3) = 2 since the harmonic mean of the divisors of 2 is 4/3.

Mathematica

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

Crossrefs

Cf. A099377, A099378, A348694.

Sequence in context: A196537 A173099 A111928 * A248054 A329421 A100985

Adjacent sequences: A348692 A348693 A348694 * A348696 A348697 A348698

Keyword

nonn

Author

Amiram Eldar, Oct 30 2021

Status

approved