a(n) = T(n,2n-6), T given by A027023.

Terms

a(0) =1a(1) =1a(2) =5a(3) =17a(4) =57a(5) =189a(6) =613a(7) =1949a(8) =6097a(9) =18825a(10) =57525a(11) =174353a(12) =525049a(13) =1573077a(14) =4693909a(15) =13960805a(16) =41415089a(17) =122603341a(18) =362343053a(19) =1069436317a(20) =3152995209a(21) =9287942097a(22) =27341397469a(23) =80443393889a(24) =236581555233a(25) =695561538977