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 A351730 #9 Feb 17 2022 14:19:26 %S A351730 1,1,4,35,604,16727,681232,38187291,2810370122,261999605819 %N A351730 Number of labeled idempotent semigroups of order n. %C A351730 a(n) is also the number of labeled idempotent monoids of order n+1 with a fixed identity. %Y A351730 Main diagonal of A058166 and A058158. %Y A351730 Cf. A023814, A058112 (isomorphism classes), A351731. %K A351730 nonn,hard,more %O A351730 0,3 %A A351730 _Andrew Howroyd_, Feb 17 2022