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

Terms

a(0) =1a(1) =1a(2) =1a(3) =1a(4) =2a(5) =2a(6) =4a(7) =6a(8) =11a(9) =18a(10) =37a(11) =66a(12) =135a(13) =265a(14) =552a(15) =1132a(16) =2410a(17) =5098a(18) =11020a(19) =23846a(20) =52233a(21) =114796a(22) =254371a(23) =565734a(24) =1265579a(25) =2841632a(26) =6408674a(27) =14502229a(28) =32935002a(29) =75021750