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A113571 Let H(n) be the reduced fraction Sum_{i=1..n} 1/i. a(n) is the least factor of H(n)'s numerator or denominator that doesn't divide either part of any earlier H(m). 0

%I

%S 1,2,6,4,10,7,14,8,9,61,22,13,26,1049,41233,16,34,19,38,11167027,

%T 18858053,23,46,138,50,34395742267,27,841,58,31,62,32,269,3583,397,

%U 1297,74,199,737281,41,82,301,86,407,1553,47,94,2323031,98,587948341,76943,2809,106,5953,51862596437,252476961434436524654789,26693,59,118,2207,122,928551009361054917576341971,347,64,2473,67,134

%N Let H(n) be the reduced fraction Sum_{i=1..n} 1/i. a(n) is the least factor of H(n)'s numerator or denominator that doesn't divide either part of any earlier H(m).

%C Also, a(n) is the first occurrence of n in A110545.

%C Conjectured last occurrence of n: 1,3,11,25,137,49,363,761,7129,7381,83711, [sic] 6617,72072,1117 (is this A001008?)

%t f[n_] := f[n] = Block[{h = k = 1}, While[ !IntegerQ[ Numerator[h]/n] && ! IntegerQ[Denominator[h]/n], k++; h = h + 1/k]; k]; Do[ f[n], {n, 84000}]; Table[ Select[ Range[84000], f[ # ] == n &][[1]], {n, 60}]

%Y Cf. A110545, A001008.

%K nonn

%O 1,2

%A _Leroy Quet_ and _Robert G. Wilson v_, Sep 29 2005

%E Entry revised (better definition, corrections, more terms) by _Don Reble_, Aug 14 2014

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Last modified May 6 06:00 EDT 2021. Contains 343580 sequences. (Running on oeis4.)