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