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

Terms

a(0) =1a(1) =1a(2) =1a(3) =3a(4) =8a(5) =31a(6) =120a(7) =511a(8) =2234a(9) =9988a(10) =45497a(11) =208435a(12) =959496a(13) =4414091a(14) =20252947a(15) =92586100a(16) =421351615a(17) =1910531192a(18) =8647504950a(19) =39194735661a(20) =178643040883a(21) =822295086652