Number of rooted trees with 3-colored leaves.

Terms

a(0) =3a(1) =3a(2) =9a(3) =28a(4) =94a(5) =328a(6) =1197a(7) =4486a(8) =17235a(9) =67429a(10) =267932a(11) =1078003a(12) =4383784a(13) =17987897a(14) =74385984a(15) =309694232a(16) =1297037177a(17) =5460726214a(18) =23098296648a(19) =98113995068a(20) =418335662448