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 A027090 #7 Oct 23 2019 17:32:36 %S A027090 1,3,9,28,84,246,714,2059,5917,16971,48633,139333,399267,1144669, %T A027090 3283839,9427981,27090715,77911897,224272499,646157234,1863317958, %U A027090 5377939756,15535195892,44913790501,129955421387,376313609029 %N A027090 a(n) = A027082(n, 2n-3). %K A027090 nonn %O A027090 2,2 %A A027090 _Clark Kimberling_