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 A111936 #22 Sep 08 2022 08:45:21
%S A111936 1,2,6,12,60,20,140,280,280,3080,9240,120120,120120,40040,80080,
%T A111936 1361360,12252240,2450448,2450448,2450448,56360304,56360304,
%U A111936 1409007600,1409007600,4227022800,4227022800,4227022800,131037706800,262075413600
%N A111936 Denominator of n-th term of the harmonic series after removal of all terms 1/m from Sum_{m=1..n} 1/m for which m contains a 9 in its decimal representation.
%C A111936 Numerator = A111935;
%C A111936 lim_{n->infinity} A111935(n)/a(n) = C < 80.
%D A111936 G. Pólya and G. Szegő, Problems and Theorems in Analysis I (Springer 1924, reprinted 1972), Part One, Chap. 3, sect. 4, Problem 124.
%e A111936 n=9: 1/1 + 1/2 + 1/3 + 1/4 + 1/5 + 1/6 + 1/7 + 1/8 + 1/10 = 789/280, therefore a(9) = 280.
%t A111936 Denominator[Accumulate[DeleteCases[Table[1/n,{n,40}],_?(MemberQ[ IntegerDigits[ Denominator[#]],9]&)]]] (* _Harvey P. Dale_, Mar 05 2013 *)
%o A111936 (Magma) a:=[k:k in [1..100]| not 9 in Intseq(k)]; [Denominator( &+[1/a[m]: m in [1..n]]): n in [1..30] ]; // _Marius A. Burtea_, Dec 29 2019
%Y A111936 Cf. A002805, A007095, A082838, A111935 (numerators).
%K A111936 nonn,base,frac
%O A111936 1,2
%A A111936 _Reinhard Zumkeller_, Aug 22 2005
%E A111936 Definition edited by _N. J. A. Sloane_, Dec 30 2019