Number of bicentered 3-valent (or boron, or binary) trees with n nodes.

Terms

a(0) =0a(1) =0a(2) =1a(3) =0a(4) =1a(5) =1a(6) =2a(7) =2a(8) =6a(9) =8a(10) =18a(11) =30a(12) =67a(13) =127a(14) =275a(15) =551a(16) =1192a(17) =2507a(18) =5475a(19) =11820a(20) =26007a(21) =57077a(22) =126686a(23) =281625a(24) =630660a(25) =1416116a(26) =3195784a(27) =7232624a(28) =16430563a(29) =37429146