Triangle read by rows: T(n,k) = number of labeled semigroups of order n with k idempotents.

Terms

a(0) =1a(1) =4a(2) =4a(3) =24a(4) =54a(5) =35a(6) =356a(7) =1044a(8) =1488a(9) =604a(10) =16585a(11) =31620a(12) =60900a(13) =57900a(14) =16727a(15) =3461916a(16) =1699290a(17) =3345420a(18) =4744380a(19) =3128880a(20) =681232a(21) =6058301508a(22) =265521354a(23) =263429355a(24) =439698420a(25) =455785470a(26) =222132666a(27) =38187291