Expansion of g.f.: Catalan(x)/Catalan(-x).

Terms

a(0) =1a(1) =2a(2) =2a(3) =8a(4) =14a(5) =64a(6) =132a(7) =640a(8) =1430a(9) =7168a(10) =16796a(11) =86016a(12) =208012a(13) =1081344a(14) =2674440a(15) =14057472a(16) =35357670a(17) =187432960a(18) =477638700a(19) =2549088256a(20) =6564120420a(21) =35223764992a(22) =91482563640a(23) =493132709888