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 A357855 #23 Jul 17 2025 14:51:02
%S A357855 1,1,3,13,829,78441,622316671,3001764349333,5926347237626029593,
%T A357855 2616519370820267981798929
%N A357855 Number of closed trails starting and ending at a fixed vertex in the complete undirected graph on n labeled vertices.
%C A357855 Trails are directed and pass through each (undirected) edge at most once in either of the two directions.
%F A357855 a(n) = Sum_{k = 0..n(n-1)/2} A357885(n,k) = 1 + Sum_{k = 1..n(n-1)/2} A357887(n,k) * k / n.
%e A357855 For n = 3, we have a(3) = 3 trails starting and ending at vertex 1: 1 (single vertex), 1->2->3->1, and 1->3->2->1.
%Y A357855 Cf. A007082, A135388, A232545, A350028, A356366, A357856, A357857, A357885, A357886, A357887.
%K A357855 nonn,more,walk
%O A357855 1,3
%A A357855 _Max Alekseyev_, Oct 16 2022
%E A357855 a(9) from _Bert Dobbelaere_, Oct 17 2022
%E A357855 a(10) from _Max Alekseyev_, Jul 17 2025