Number of forests with at most n unlabeled nodes.

Terms

a(0) =1a(1) =2a(2) =4a(3) =7a(4) =13a(5) =23a(6) =43a(7) =80a(8) =156a(9) =309a(10) =638a(11) =1348a(12) =2949a(13) =6607a(14) =15206a(15) =35720a(16) =85625a(17) =208588a(18) =515787a(19) =1291316a(20) =3269194a(21) =8355832a(22) =21539988a(23) =55942920a(24) =146271594a(25) =384746580a(26) =1017522228a(27) =2704227858a(28) =7219183490a(29) =19351410860