Number of rooted unlabeled trees on n nodes having a primary branch.

Terms

a(0) =0a(1) =1a(2) =1a(3) =3a(4) =6a(5) =17a(6) =37a(7) =102a(8) =239a(9) =658a(10) =1607a(11) =4425a(12) =11185a(13) =30990a(14) =80070a(15) =222731a(16) =586218a(17) =1638333a(18) =4370721a(19) =12262003a(20) =33077327a(21) =93128828a(22) =253454781a(23) =715784848a(24) =1962537755a(25) =5557799401a(26) =15332668869a(27) =43527249088a(28) =120716987723