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 A109140 #4 Apr 28 2021 12:39:32 %S A109140 1,1,3,7,31,69,307,683,3039,18917,40873,264155,1097493,2459141, %T A109140 10934057,68063483,419314955,906693393,5859475313,24344594645, %U A109140 54548664603,351636582263,1461094993655,9118206544193 %N A109140 Denominators associated with A109139. %Y A109140 Cf. A109139. %K A109140 nonn,frac %O A109140 0,3 %A A109140 _Giorgio Balzarotti_, Aug 18 2005