G.f. A(x) satisfies A(x) = (1 + x*A(x))*(1 + x^3*A(x)^4).

Terms

a(0) =1a(1) =1a(2) =1a(3) =2a(4) =7a(5) =22a(6) =61a(7) =172a(8) =528a(9) =1695a(10) =5447a(11) =17486a(12) =56778a(13) =187064a(14) =622149a(15) =2080325a(16) =6990670a(17) =23621143a(18) =80230388a(19) =273687898a(20) =937072049a(21) =3219316096a(22) =11095261035a(23) =38351414036a(24) =132915860364a(25) =461770505371