a(n) = T(2n,n-1), T given by A026519.

Terms

a(0) =1a(1) =2a(2) =9a(3) =32a(4) =130a(5) =516a(6) =2107a(7) =8632a(8) =35703a(9) =148390a(10) =619850a(11) =2598960a(12) =10933507a(13) =46124274a(14) =195055005a(15) =826617216a(16) =3509650697a(17) =14926011714a(18) =63572290247a(19) =271125967840