G.f.: A(x) = (x-2*x^2-2*x^3-(1+x)*sqrt(1-4*x^2)+sqrt(1-4*x^6))/(2*x^2).

Terms

a(0) =1a(1) =1a(2) =1a(3) =2a(4) =5a(5) =5a(6) =14a(7) =14a(8) =41a(9) =42a(10) =132a(11) =132a(12) =429a(13) =429a(14) =1428a(15) =1430a(16) =4862a(17) =4862a(18) =16796a(19) =16796a(20) =58781a(21) =58786a(22) =208012a(23) =208012a(24) =742900a(25) =742900a(26) =2674426a(27) =2674440a(28) =9694845a(29) =9694845