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 A069220 #16 Jun 07 2020 15:23:23
%S A069220 1,1,2,3,12,5,20,105,280,63,2520,385,27720,6435,8008,45045,720720,
%T A069220 85085,4084080,2909907,3695120,1322685,5173168,37182145,118982864,
%U A069220 128707425,2974571600,717084225,80313433200,215656441,2329089562800
%N A069220 Denominator of Sum_{1<=k<=n, gcd(k,n)=1} 1/k.
%H A069220 Seiichi Manyama, <a href="/A069220/b069220.txt">Table of n, a(n) for n = 1..2310</a>
%F A069220 G.f. A(x) (for fractions) satisfies: A(x) = -log(1 - x)/(1 - x) - Sum_{k>=2} A(x^k)/k. - _Ilya Gutkovskiy_, Mar 31 2020
%t A069220 Table[s=0; Do[If[GCD[i, n]==1, s=s+1/i], {i, n}]; Denominator[s], {n, 1, 35}]
%t A069220 Table[Denominator[Total[1/Select[Range[n],GCD[n,#]==1&]]],{n,40}] (* _Harvey P. Dale_, Jun 07 2020 *)
%o A069220 (PARI) for(n=1,40,print1(denominator(sum(k=1,n,if(gcd(k,n)==1,1/k))),","))
%Y A069220 Cf. A017666, A002805.
%Y A069220 Cf. A093600 (numerator of this sum).
%Y A069220 Also denominators of row sums of A111879/A111880. For the numerators see A111881.
%K A069220 nonn,frac
%O A069220 1,3
%A A069220 Sharon Sela (sharonsela(AT)hotmail.com), Apr 12 2002
%E A069220 More terms from _Jason Earls_, Apr 14 2002