Number of unlabeled rooted trees with at most n nodes.

Terms

a(0) =1a(1) =2a(2) =4a(3) =8a(4) =17a(5) =37a(6) =85a(7) =200a(8) =486a(9) =1205a(10) =3047a(11) =7813a(12) =20299a(13) =53272a(14) =141083a(15) =376464a(16) =1011311a(17) =2732470a(18) =7421146a(19) =20247374a(20) =55469206a(21) =152524387a(22) =420807242a(23) =1164532226a(24) =3231706871a(25) =8991343381a(26) =25075077710a(27) =70082143979a(28) =196268698287a(29) =550695545884