a(n) = T(n,2n-7), T given by A027023.

Terms

a(0) =1a(1) =3a(2) =9a(3) =31a(4) =105a(5) =351a(6) =1157a(7) =3755a(8) =12013a(9) =37951a(10) =118613a(11) =367383a(12) =1129345a(13) =3449823a(14) =10482869a(15) =31713863a(16) =95589753a(17) =287224199a(18) =860773781a(19) =2573894583a(20) =7681972113a(21) =22890634939a(22) =68116073369a(23) =202458285647a(24) =601159897137