Number of unlabeled n-node simple graphs with at most one cycle in each connected component.

Terms

a(0) =1a(1) =1a(2) =2a(3) =4a(4) =9a(5) =19a(6) =46a(7) =108a(8) =273a(9) =696a(10) =1836a(11) =4896a(12) =13323a(13) =36541a(14) =101323a(15) =282693a(16) =793697a(17) =2237982a(18) =6335978a(19) =17992622a(20) =51235887a(21) =146228734a(22) =418181860a(23) =1197972026a(24) =3437159492a(25) =9875198568a(26) =28407202891a(27) =81807809714a(28) =235831978115a(29) =680478488927