a(n) is the number of rooted binary trees with minimal Sackin index and n leaves.

Terms

a(0) =1a(1) =1a(2) =1a(3) =1a(4) =1a(5) =2a(6) =1a(7) =1a(8) =1a(9) =3a(10) =3a(11) =5a(12) =3a(13) =3a(14) =1a(15) =1a(16) =1a(17) =4a(18) =6a(19) =14a(20) =17a(21) =27a(22) =28a(23) =35a(24) =28a(25) =27a(26) =17a(27) =14a(28) =6a(29) =4