G.f. A(x) satisfies: A(x)^2 = A(x^2) + 6*x.

Terms

a(0) =1a(1) =3a(2) =-3a(3) =9a(4) =-33a(5) =126a(6) =-513a(7) =2214a(8) =-9876a(9) =45045a(10) =-209493a(11) =990198a(12) =-4741191a(13) =22946247a(14) =-112079214a(15) =551793303a(16) =-2735330190a(17) =13641353118a(18) =-68394016548a(19) =344539469889