Number of shapes of height-balanced AVL trees with n nodes.

Terms

a(0) =1a(1) =1a(2) =2a(3) =1a(4) =4a(5) =6a(6) =4a(7) =17a(8) =32a(9) =44a(10) =60a(11) =70a(12) =184a(13) =476a(14) =872a(15) =1553a(16) =2720a(17) =4288a(18) =6312a(19) =9004a(20) =16088a(21) =36900a(22) =82984a(23) =174374a(24) =346048a(25) =653096a(26) =1199384a(27) =2160732a(28) =3812464a(29) =6617304