Number of free planar polyenoids with n nodes.

Terms

a(0) =1a(1) =1a(2) =1a(3) =3a(4) =4a(5) =12a(6) =26a(7) =77a(8) =204a(9) =624a(10) =1817a(11) =5585a(12) =17007a(13) =52803a(14) =164001a(15) =514009a(16) =1615044a(17) =5100324a(18) =16152134a(19) =51324864