Number of simple unlabeled graphs on n nodes with connected components that are trees or cycles.

Terms

a(0) =1a(1) =1a(2) =2a(3) =4a(4) =8a(5) =14a(6) =28a(7) =52a(8) =104a(9) =206a(10) =429a(11) =903a(12) =1982a(13) =4430a(14) =10206a(15) =23966a(16) =57522a(17) =140236a(18) =347302a(19) =870682a(20) =2207819a(21) =5651437a(22) =14590703a(23) =37948338a(24) =99358533a(25) =261684141a(26) =692906575a(27) =1843601797a(28) =4926919859a(29) =13220064562