G.f. satisfies A(x) = 1 + 2*x*A(x) + x^4*A(x)^4.

Terms

a(0) =1a(1) =2a(2) =4a(3) =8a(4) =17a(5) =42a(6) =124a(7) =408a(8) =1380a(9) =4616a(10) =15184a(11) =49568a(12) =162518a(13) =539580a(14) =1818184a(15) =6203088a(16) =21339916a(17) =73776024a(18) =255853744a(19) =889678688a(20) =3102779785a(21) =10856555130a(22) =38115293308a(23) =134243564056a(24) =474159194316