a(n) = 3*C(4*n-2,2*n)/(2*n+1) - 2*0^n.

Terms

a(0) =1a(1) =1a(2) =9a(3) =90a(4) =1001a(5) =11934a(6) =149226a(7) =1931540a(8) =25662825a(9) =347993910a(10) =4796857230a(11) =67016296620a(12) =946844533674