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 A357857 #17 Oct 19 2022 07:16:49 %S A357857 1,4,21,232,14425,3653196,17705858989,261353065517776, %T A357857 241809117107232026097 %N A357857 Number of (open and closed) trails in the complete undirected graph on n labeled vertices. %C A357857 Trails are directed and pass through each (undirected) edge at most once in either of the two directions. %F A357857 a(n) = n * A357855(n) + n * (n-1) * A357856(n). %Y A357857 Cf. A007082, A135388, A232545, A350028, A356366, A357855, A357856, A357885, A357886, A357887. %K A357857 nonn,more,walk %O A357857 1,2 %A A357857 _Max Alekseyev_, Oct 16 2022 %E A357857 a(9) from _Bert Dobbelaere_, Oct 17 2022