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Numbers k such that lcm(1,2,3,...,k)/13 equals the denominator of the k-th harmonic number H(k).
12

%I #11 Apr 02 2022 15:29:35

%S 156,157,158,159,160,161,27380,27381,27382,27383,27384,27385,27386,

%T 27387,27388,27389,27390,27391,27392,27393,27394,27395,27396,27397,

%U 27398,27399,27400,27401,27402,27403,27404,27405,27406,27407,27408

%N Numbers k such that lcm(1,2,3,...,k)/13 equals the denominator of the k-th harmonic number H(k).

%C When 13 occurs in A110566.

%H Jinyuan Wang, <a href="/A112818/b112818.txt">Table of n, a(n) for n = 1..851</a>

%t a = h = 1; t = {}; Do[a = LCM[a, n]; h = h + 1/n; b = a/Denominator[h]; If[b == 13, AppendTo[t, n]], {n, 27408}]; t

%t With[{tk=Table[{LCM@@Range[k]/13,Denominator[HarmonicNumber[k]]},{k,28000}]},Position[ tk,_?(#[[1]]==#[[2]]&),1,Heads->False]]//Flatten (* _Harvey P. Dale_, Apr 02 2022 *)

%Y Cf. A002805, A003418, A110566.

%Y Cf. A098464, A112813, A112814, A112815, A112816, A112817, 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