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 A161138 #4 Jan 15 2022 21:37:12 %S A161138 1,3,9,18,80,196,554,1824,2292,7218,45522,288135,660113,3201130, %T A161138 10512530,17675063,191230544,207521990 %N A161138 Main diagonal of the triangular array A161136. %F A161138 a(m) = A161136(m,m). %Y A161138 Cf. A161135, A161136, A161137. %K A161138 more,nonn %O A161138 1,2 %A A161138 _Max Alekseyev_, Jun 02 2009