a(n) = T(2n+1,n+4), T given by A026736.

Terms

a(0) =1a(1) =9a(2) =55a(3) =287a(4) =1381a(5) =6343a(6) =28313a(7) =124083a(8) =537242a(9) =2307118a(10) =9852240a(11) =41910428a(12) =177807902a(13) =752981956a(14) =3184773246a(15) =13459063660a(16) =56849094136a(17) =240047748038