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Numbers k such that lcm(1,2,3,...,k)/9 equals the denominator of the k-th harmonic number H(k).
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%I #16 Jan 31 2021 02:38:14

%S 63,64,65,69,70,71,189,190,191,192,193,194,195,196,197,207,208,209,

%T 210,211,212,213,214,215,1701,1702,1703,1704,1705,1706,1707,1708,1709,

%U 1710,1711,1712,1713,1714,1715,1716,1717,1718,1719,1720,1721,1722,1723,1724

%N Numbers k such that lcm(1,2,3,...,k)/9 equals the denominator of the k-th harmonic number H(k).

%C When 9 occurs in A110566.

%H Amiram Eldar, <a href="/A112816/b112816.txt">Table of n, a(n) for n = 1..10000</a> (terms 1..1483 from Jinyuan Wang)

%t f[n_] := LCM @@ Range[n]/Denominator[ HarmonicNumber[n]]; Select[ Range[1724], f[ # ] == 9 &]

%Y Cf. A002805, A003418, A110566.

%Y Cf. A098464, A112813, A112814, A112815, A112817, A112818, A112819, A112820, A112821, A112822.

%K nonn

%O 1,1

%A _Robert G. Wilson v_, Sep 17 2005

%E Definition corrected by _Jinyuan Wang_, May 03 2020