Number of 3-covers of an unlabeled n-set.

Terms

a(0) =1a(1) =3a(2) =9a(3) =23a(4) =51a(5) =103a(6) =196a(7) =348a(8) =590a(9) =960a(10) =1506a(11) =2290a(12) =3393a(13) =4905a(14) =6945a(15) =9651a(16) =13185a(17) =17739a(18) =23542a(19) =30846a(20) =39954a(21) =51206a(22) =64986a(23) =81730a(24) =101935a(25) =126141a(26) =154967a(27) =189093a(28) =229269a(29) =276325