Number of hybrid binary trees with n internal nodes.

Terms

a(0) =1a(1) =2a(2) =7a(3) =31a(4) =154a(5) =820a(6) =4575a(7) =26398a(8) =156233a(9) =943174a(10) =5785416a(11) =35955297a(12) =225914342a(13) =1432705496a(14) =9158708775a(15) =58954911423a(16) =381806076426