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

Terms

a(0) =1a(1) =2a(2) =2a(3) =10a(4) =18a(5) =98a(6) =210a(7) =1194a(8) =2786a(9) =16258a(10) =39906a(11) =236938a(12) =601458a(13) =3615330a(14) =9399858a(15) =57024426a(16) =150947010a(17) =922283522a(18) =2475603138a(19) =15212318730a(20) =41290579410a(21) =254909413218a(22) =698230131858