Number of 2-linear trees on n nodes.

Terms

a(0) =0a(1) =0a(2) =0a(3) =0a(4) =0a(5) =1a(6) =3a(7) =10a(8) =24a(9) =56a(10) =114a(11) =224a(12) =411a(13) =733a(14) =1252a(15) =2091a(16) =3393a(17) =5408a(18) =8440a(19) =12982a(20) =19650a(21) =29388a(22) =43394a(23) =63430a(24) =91754a(25) =131584a(26) =187057a(27) =263932a(28) =369624a(29) =514253