Number of rooted planar n-trees whose number of leaves is equal to 2 modulo 3.

Terms

a(0) =0a(1) =0a(2) =1a(3) =3a(4) =6a(5) =11a(6) =30a(7) =126a(8) =519a(9) =1836a(10) =5877a(11) =18866a(12) =65472a(13) =242463a(14) =905425a(15) =3307371a(16) =11889414a(17) =42930441a(18) =157641714a(19) =586908936a(20) =2194106568a(21) =8189323686a(22) =30541703733a(23) =114219616809a(24) =429214875498