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 A212718 #4 May 25 2012 14:32:48
%S A212718 1,3,12,84,28,42,168,280,3640,32760,32760,32760,4680,1170,4680,145080,
%T A212718 145080,145080,145080,1015560,4062240,4062240,4062240,4062240,4062240,
%U A212718 4062240,4062240,4062240,4062240,4062240,2031120,2031120,1015560,3046680,6093360,6093360
%N A212718 Denominator of Sum_{k=1..n} 1/sigma(k).
%e A212718 1, 4/3, 19/12, 145/84, 53/28, 83/42, 353/168, …
%p A212718 with(numtheory): a:=n->numer(sum(1/sigma(k), k=1..n)): seq(a(n), n=1..50);
%t A212718 Denominator[Table[Sum[1/DivisorSigma[1,k],{k,1,n}],{n,1,50}]]
%Y A212718 Cf. A000203, A212717.
%K A212718 nonn,frac
%O A212718 1,2
%A A212718 _Michel Lagneau_, May 25 2012