Number of mobiles (circular rooted trees) with n nodes and 3 leaves.

Terms

a(0) =1a(1) =3a(2) =8a(3) =19a(4) =37a(5) =66a(6) =110a(7) =172a(8) =257a(9) =371a(10) =518a(11) =705a(12) =939a(13) =1226a(14) =1574a(15) =1992a(16) =2487a(17) =3069a(18) =3748a(19) =4533a(20) =5435a(21) =6466a(22) =7636a(23) =8958a(24) =10445a(25) =12109a(26) =13964a(27) =16025a(28) =18305a(29) =20820