Number of trees with n unlabeled nodes.

Terms

a(0) =1a(1) =1a(2) =1a(3) =1a(4) =2a(5) =3a(6) =6a(7) =11a(8) =23a(9) =47a(10) =106a(11) =235a(12) =551a(13) =1301a(14) =3159a(15) =7741a(16) =19320a(17) =48629a(18) =123867a(19) =317955a(20) =823065a(21) =2144505a(22) =5623756a(23) =14828074a(24) =39299897a(25) =104636890a(26) =279793450a(27) =751065460a(28) =2023443032a(29) =5469566585