This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A112821 #9 Mar 04 2018 20:53:04
%S A112821 343,344,345,346,347,348,349,350,351,352,353,354,355,356,357,358,359,
%T A112821 360
%N A112821 Numbers n such that lcm(1,2,3,...,n)/19 equals the denominator of the n-th harmonic number H(n).
%C A112821 Positions where 19 occurs in A110566.
%H A112821 Tanya Khovanova, <a href="http://www.tanyakhovanova.com/RecursiveSequences/NonRecursions.html">Non Recursions</a>
%t A112821 a = h = 1; t = {}; Do[a = LCM[a, n]; h = h + 1/n; If[a/Denominator[h] == 19, AppendTo[t, n]], {n, 10^6}]; t
%t A112821 Select[Range[500],Denominator[HarmonicNumber[#]]==LCM@@Range[#]/19&] (* _Harvey P. Dale_, Jan 29 2012 *)
%Y A112821 Cf. A002805, A003418, A110566.
%Y A112821 Cf. A098464, A112813, A112814, A112815, A112816, A112817, A112818, A112819, A112820, A112822.
%K A112821 nonn,more
%O A112821 1,1
%A A112821 _Robert G. Wilson v_, Sep 17 2005
%E A112821 Definition corrected by _Max Alekseyev_, Mar 03 2007