Number of ordered trees with n edges and having no branches of length 2.

Terms

a(0) =1a(1) =1a(2) =1a(3) =3a(4) =7a(5) =18a(6) =47a(7) =129a(8) =362a(9) =1038a(10) =3022a(11) =8917a(12) =26600a(13) =80098a(14) =243132a(15) =743180a(16) =2285597a(17) =7067271a(18) =21957947a(19) =68517606a(20) =214633572a(21) =674712991a(22) =2127790260a(23) =6729876378a(24) =21342679122a(25) =67851885121a(26) =216204228642a(27) =690371596017