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

Terms

a(0) =1a(1) =1a(2) =2a(3) =8a(4) =26a(5) =127a(6) =478a(7) =2536a(8) =10250a(9) =56900a(10) =239880a(11) =1370272a(12) =5940054a(13) =34607146a(14) =153018932a(15) =904441648a(16) =4058644842a(17) =24254529036a(18) =110096276440a(19) =663665021280