%I #15 Jan 31 2021 02:38:20
%S 6,7,8,18,19,25,26,54,55,56,57,58,59,60,61,62,72,73,74,75,76,169,170,
%T 171,172,173,174,175,176,177,178,179,180,181,182,183,184,185,186,187,
%U 188,216,217,218,219,220,221,222,223,224,225,226,227,228,229,230,231
%N Numbers k such that lcm(1,2,3,...,k)/3 equals the denominator of the k-th harmonic number H(k).
%C When 3 occurs in A110566.
%H Amiram Eldar, <a href="/A112813/b112813.txt">Table of n, a(n) for n = 1..10000</a>
%t f[n_] := LCM @@ Range[n]/Denominator[ HarmonicNumber[n]]; Select[ Range[231], f[ # ] == 3 &]
%o (PARI) isok(n) = lcm(vector(n, i, i)) == 3*denominator(sum(i=1, n, 1/i)); \\ _Michel Marcus_, Mar 07 2018
%Y Cf. A002805, A003418, A110566.
%Y Cf. A098464, A112814, A112815, A112816, A112817, A112818, A112819, A112820, A112821, A112822.
%K nonn
%O 1,1
%A _Robert G. Wilson v_, Sep 17 2005