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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. 2

%I #11 Oct 30 2021 10:41:56

%S 1,3,2,7,24,11,4,21,10,19,258,23,9,39,8,31,402,55,37,57,26,43,3836,47,

%T 216,99,34,124,4844,59,16,93,86,67,76,71,73,111,125,79,978,83,7196,

%U 129,58,411,7868,155,52,447,101,63,1266,107,109,372,74,519,9884,203

%N 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.

%H Amiram Eldar, <a href="/A348695/b348695.txt">Table of n, a(n) for n = 1..1000</a>

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

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

%t 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]

%Y Cf. A099377, A099378, A348694.

%K nonn

%O 1,2

%A _Amiram Eldar_, Oct 30 2021

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Last modified May 21 12:09 EDT 2024. Contains 372736 sequences. (Running on oeis4.)