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 A126196 #36 Aug 24 2021 13:08:45
%S A126196 7,546,1092,1755,3510,4896,52447,670668
%N A126196 Numbers k such that gcd(A001008(k), A001008(floor(k/2))) > 1.
%C A126196 Note a connection to the Wieferich primes A001220: a(2) = (A001220(1) - 1)/2, a(3) = A001220(1) - 1, a(4) = (A001220(2) - 1)/2, a(5) = A001220(2) - 1. [Comment regarding a(2) added by _Kevin J. Gomez_, Jul 11 2017]
%C A126196 a(9) > 840000. - _Giovanni Resta_, May 13 2016
%t A126196 Select[Range[5000], GCD @@ Numerator@ HarmonicNumber@{#, Floor[#/2]} > 1 &] (* _Giovanni Resta_, May 13 2016 *)
%o A126196 (PARI) a001008(n)=numerator(sum(i=1, n, 1/i))
%o A126196 for(n=1, 1e6, if(gcd(a001008(n), a001008(n/2)) > 1, print1(n, ", "))) \\ _Felix Fröhlich_, Aug 08 2014
%Y A126196 The corresponding GCDs are given by A126197.
%Y A126196 Cf. A001008, A001220, A002805, A058312, A058313, A074791, A121594, A125581.
%K A126196 nonn,more
%O A126196 1,1
%A A126196 _Max Alekseyev_ and _Tanya Khovanova_, Mar 07 2007, corrected Mar 10 2007
%E A126196 a(8) from _Giovanni Resta_, May 13 2016