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 A281086 #7 Jan 04 2020 16:34:16
%S A281086 1,1,2,3,12,20,20,70,840,504,2520,27720,27720,51480,360360,180180,
%T A281086 720720,1361360,4084080,77597520,15519504,470288,5173168,356948592,
%U A281086 1784742960,686439600,26771144400,80313433200,80313433200,2329089562800,2329089562800,36100888223400
%N A281086 Denominator of sum of reciprocals of numbers less than n that do not divide n.
%F A281086 a(n) = denominator(H_n - Sum_{d|n} 1/d), where H_n is the n-th harmonic number.
%F A281086 a(n) = denominator(A001008(n)/A002805(n) - A000203(n)/n).
%F A281086 Denominators of coefficients in expansion of -log(1 - x)/(1 - x) - Sum_{k>=1} log(1/(1 - x^k)).
%e A281086 a(6) = 20 because 6 has 4 divisors {1,2,3,6} therefore 2 non-divisors {4,5} and 1/4 + 1/5 = 9/20.
%e A281086 0, 0, 1/2, 1/3, 13/12, 9/20, 29/20, 59/70, 1163/840, 569/504, 4861/2520, 21341/27720, 58301/27720, 79139/51480, 619181/360360, 260041/180180, ...
%t A281086 Table[Denominator[HarmonicNumber[n] - DivisorSigma[-1, n]], {n, 1, 32}]
%t A281086 Table[Denominator[HarmonicNumber[n] - DivisorSigma[1, n]/n], {n, 1, 32}]
%t A281086 Table[Denominator[Total[1/Complement[Range[n],Divisors[n]]]],{n,40}] (* _Harvey P. Dale_, Jan 04 2020 *)
%Y A281086 Cf. A000203, A001008, A002805, A017665, A017666, A024816, A277791, A281085 (numerators).
%K A281086 nonn,frac
%O A281086 1,3
%A A281086 _Ilya Gutkovskiy_, Jan 14 2017