Number of 4-level rooted trees with n leaves.

Terms

a(0) =1a(1) =1a(2) =4a(3) =10a(4) =30a(5) =75a(6) =206a(7) =518a(8) =1344a(9) =3357a(10) =8429a(11) =20759a(12) =51044a(13) =123973a(14) =299848a(15) =719197a(16) =1716563a(17) =4070800a(18) =9607797a(19) =22555988a(20) =52718749a(21) =122655485a(22) =284207304a(23) =655894527a(24) =1508046031a(25) =3454808143a(26) =7887768997a(27) =17949709753a(28) =40719611684a(29) =92096461012