Unlabeled trees with n nodes rooted at 2 indistinguishable roots that are leaves.

Terms

a(0) =0a(1) =1a(2) =1a(3) =2a(4) =4a(5) =10a(6) =24a(7) =63a(8) =164a(9) =444a(10) =1204a(11) =3328a(12) =9233a(13) =25865a(14) =72734a(15) =205656a(16) =583320a(17) =1660318a(18) =4737540a(19) =13551165a(20) =38837535a(21) =111512229a(22) =320681604a(23) =923528963a(24) =2663057582a(25) =7688068638a(26) =22218350303a(27) =64272720521a(28) =186091334380a(29) =539237928902