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 A361912 #21 Apr 03 2023 21:09:18 %S A361912 1,1,2,4,10,28,93,354,1621,9110,64801,595976,7204091,115561423, %T A361912 2473540433,70853213144,2720354016419,140170631441858, %U A361912 9702605436760235,903309202327818566,113234129823368903523,19137461395401601912043,4366007821745938984134203 %N A361912 The number of unlabeled graded posets with n elements. %C A361912 A partially ordered set is graded if all maximal chains have the same length. This is called tiered by some authors. %H A361912 Andrew Howroyd, <a href="/A361912/b361912.txt">Table of n, a(n) for n = 0..40</a> %o A361912 (Sage) sum(1 for P in posets(n) if P.is_graded()) %o A361912 (PARI) \\ See PARI link in A361957 for program code. %o A361912 A361912seq(20) \\ _Andrew Howroyd_, Apr 03 2023 %Y A361912 Row sums of A361957. %Y A361912 Cf. A000112, A223911 (labeled), A001833, A361920, A361959 (connected). %K A361912 nonn %O A361912 0,3 %A A361912 _Martin Rubey_, Mar 29 2023 %E A361912 Terms a(8) and beyond from _Andrew Howroyd_, Mar 30 2023