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 A357856 #15 Oct 19 2022 07:14:06
%S A357856 0,1,2,15,514,106085,317848626,4238195548627,2617666555119413330
%N A357856 Number of trails between two fixed distinct vertices in the complete undirected graph on n labeled vertices.
%C A357856 Trails are directed and pass through each (undirected) edge at most once in either of the two directions.
%F A357856 a(n) = Sum_{k = 0..n(n-1)/2} A357886(n,k).
%Y A357856 Cf. A007082, A135388, A232545, A350028, A356366, A357855, A357857, A357885, A357886, A357887.
%K A357856 nonn,more,walk
%O A357856 1,3
%A A357856 _Max Alekseyev_, Oct 16 2022
%E A357856 a(9) from _Bert Dobbelaere_, Oct 17 2022