Number of rooted planar n-trees whose number of leaves is equal to 1 modulo 3.

Terms

a(0) =0a(1) =1a(2) =1a(3) =1a(4) =2a(5) =11a(6) =51a(7) =177a(8) =519a(9) =1513a(10) =5042a(11) =18866a(12) =71270a(13) =257974a(14) =905425a(15) =3193737a(16) =11578842a(17) =42930441a(18) =159998493a(19) =593445318a(20) =2194106568a(21) =8138471667a(22) =30399156174a(23) =114219616809a(24) =430344635913