a(n) = T(2n, n+2), T given by A027935.

Terms

a(0) =1a(1) =16a(2) =92a(3) =365a(4) =1204a(5) =3588a(6) =10093a(7) =27476a(8) =73440a(9) =194345a(10) =511576a(11) =1342936a(12) =3520457a(13) =9222440a(14) =24151764a(15) =63238773a(16) =165571628a(17) =433484476a(18) =1134891605a(19) =2971201740a(20) =7778726776