Number of shapes of height-balanced AVL trees of height at most 6 with n nodes.

Terms

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