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 A082688 #22 Dec 14 2017 05:22:57
%S A082688 2,12,60,840,2520,27720,360360,144144,2450448,232792560,232792560,
%T A082688 5354228880,26771144400,11473347600,332727080400,20629078984800,
%U A082688 20629078984800,144403552893600,5342931457063200,5342931457063200
%N A082688 Denominator of Sum_{k=1..n} 1/(n+k).
%H A082688 T. D. Noe, <a href="/A082688/b082688.txt">Table of n, a(n) for n=1..100</a>
%F A082688 limit n ->infinity Sum_{k=1..n} 1/(n+k) = log(2).
%F A082688 Denominator of Psi(2*n+1)-Psi(n+1). - _Vladeta Jovovic_, Aug 24 2003
%e A082688 1/2, 7/12, 37/60, 533/840, 1627/2520, 18107/27720, 237371/360360, ...
%t A082688 Table[HarmonicNumber[2 n] - HarmonicNumber[n], {n, 20}] // Denominator (* _Eric W. Weisstein_, Dec 14 2017 *)
%o A082688 (PARI) a(n) = denominator(sum(k=1, n, 1/(n+k))); \\ _Michel Marcus_, Dec 14 2017
%Y A082688 Cf. A058312, A082687 (numerators).
%K A082688 frac,nonn,easy
%O A082688 1,1
%A A082688 _Benoit Cloitre_, Apr 12 2003