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 A027172 #8 Oct 24 2019 19:13:29 %S A027172 5,21,78,285,1048,3892,14584,55053,209064,797808,3056870,11752676, %T A027172 45316898,175175818,678639148,2634146413,10241938408,39882831448, %U A027172 155519160718,607181138848,2373227900938,9285480209458,36364319046898 %N A027172 a(n) = (1/2) * A027170(2n, n). %C A027172 A027175(n) + 2. %K A027172 nonn %O A027172 1,1 %A A027172 _Clark Kimberling_