Subtrees in rooted plane trees on n nodes.

Terms

a(0) =1a(1) =3a(2) =12a(3) =52a(4) =236a(5) =1109a(6) =5366a(7) =26639a(8) =135300a(9) =701269a(10) =3700400a(11) =19834973a(12) =107784622a(13) =592705377a(14) =3292970302a(15) =18458954896a(16) =104276682820a(17) =593056996445