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 A361921 #9 Mar 31 2023 05:00:05 %S A361921 0,1,1,0,1,0,1,0,2,0,5,0,11 %N A361921 The number of unlabeled bounded Eulerian posets with n elements. %C A361921 A graded partially ordered set is Eulerian if every nontrivial interval has the same number of elements of even rank as of odd rank. It is bounded if it has a unique maximal and a unique minimal element. %H A361921 Wikipedia, <a href="https://en.wikipedia.org/wiki/Eulerian_poset">Eulerian poset</a> %o A361921 (Sage) sum(1 for P in posets(n-2) if (Q := P.with_bounds()).is_graded() and Q.is_eulerian()) %K A361921 nonn,hard,more %O A361921 0,9 %A A361921 _Martin Rubey_, Mar 30 2023