Number of terms in n-th derivative of a function composed with itself 3 times.

Terms

a(0) =1a(1) =1a(2) =3a(3) =6a(4) =13a(5) =23a(6) =44a(7) =74a(8) =129a(9) =210a(10) =345a(11) =542a(12) =858a(13) =1310a(14) =2004a(15) =2996a(16) =4467a(17) =6540a(18) =9552a(19) =13744a(20) =19711a(21) =27943a(22) =39452a(23) =55172a(24) =76865a(25) =106200a(26) =146173a(27) =199806a(28) =272075a(29) =368247