Number of 4-ary rooted trees with n nodes and height exactly 3.

Terms

a(0) =0a(1) =0a(2) =0a(3) =1a(4) =2a(5) =4a(6) =6a(7) =8a(8) =9a(9) =11a(10) =11a(11) =12a(12) =11a(13) =11a(14) =9a(15) =8a(16) =6a(17) =5a(18) =3a(19) =2a(20) =1a(21) =1