A335703(2n).

Terms

a(0) =1a(1) =3a(2) =9a(3) =30a(4) =95a(5) =326a(6) =1195a(7) =4478a(8) =17251a(9) =67326a(10) =266331a(11) =1058146a(12) =4216075a(13) =16808282a(14) =67130923a(15) =268281390a(16) =1072424939