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Number of labeled idempotent semigroups of order n.
3

%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