a(n) = T(n,2n-4), T given by A027052.

Terms

a(0) =1a(1) =1a(2) =3a(3) =11a(4) =35a(5) =107a(6) =319a(7) =935a(8) =2713a(9) =7825a(10) =22491a(11) =64523a(12) =184945a(13) =530001a(14) =1519151a(15) =4356471a(16) =12501301a(17) =35901325a(18) =103188123a(19) =296844379a(20) =854701935a(21) =2463133311a(22) =7104685935a(23) =20510632575a(24) =59262772629a(25) =171373598341a(26) =495968905267