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

Terms

a(0) =1a(1) =1a(2) =0a(3) =1a(4) =1a(5) =1a(6) =2a(7) =4a(8) =5a(9) =10a(10) =19a(11) =36a(12) =68a(13) =138a(14) =277a(15) =581a(16) =1218a(17) =2591a(18) =5545a(19) =12026a(20) =26226a(21) =57719a(22) =127685a(23) =284109a(24) =634919a(25) =1425516a(26) =3212890a(27) =7269605a(28) =16504439a(29) =37592604