Triangle T(n,k) (n >= 1, k >= 1) giving filtration of bigrading of Hopf algebra of rooted trees.

Terms

a(0) =1a(1) =1a(2) =1a(3) =2a(4) =1a(5) =1a(6) =3a(7) =3a(8) =2a(9) =1a(10) =8a(11) =5a(12) =4a(13) =2a(14) =1a(15) =16a(16) =13a(17) =9a(18) =6a(19) =3a(20) =1a(21) =41a(22) =28a(23) =21a(24) =13a(25) =8a(26) =3a(27) =1a(28) =98a(29) =71