a(n) = T(n,2n-5), T given by A027023.

Terms

a(0) =1a(1) =3a(2) =9a(3) =31a(4) =101a(5) =319a(6) =985a(7) =2991a(8) =8973a(9) =26687a(10) =78877a(11) =232083a(12) =680645a(13) =1991487a(14) =5817073a(15) =16971415a(16) =49474389a(17) =144149959a(18) =419869065a(19) =1222785111a(20) =3561052305a(21) =10371483259a(22) =30211361481a(23) =88022087975a(24) =256521698097a(25) =747794233779