Triangle of coefficients of generating function of ternary rooted trees of height at most n.

Terms

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