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

Terms

a(0) =1a(1) =1a(2) =-3a(3) =-6a(4) =35a(5) =87a(6) =-588a(7) =-1578a(8) =11511a(9) =32223a(10) =-245883a(11) =-706824a(12) =5556564a(13) =16267508a(14) =-130617600a(15) =-387533058a(16) =3161190783a(17) =9474886287a(18) =-78241316361a(19) =-236394953670