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

Terms

a(0) =1a(1) =1a(2) =6a(3) =18a(4) =110a(5) =498a(6) =3366a(7) =17282a(8) =122958a(9) =672930a(10) =4938758a(11) =28103730a(12) =210595182a(13) =1230391058a(14) =9358456230a(15) =55727128866a(16) =428643977422