Infima closed sets in rooted plane trees on n nodes.

Terms

a(0) =1a(1) =3a(2) =13a(3) =63a(4) =326a(5) =1769a(6) =9964a(7) =57843a(8) =344203a(9) =2090470a(10) =12912988a(11) =80899801a(12) =512896540a(13) =3284651548a(14) =21217493460a(15) =138080484819a(16) =904454380446