a(n) = T(n, 2n-3), T given by A027023.

Terms

a(0) =1a(1) =3a(2) =9a(3) =27a(4) =77a(5) =215a(6) =597a(7) =1655a(8) =4593a(9) =12775a(10) =35629a(11) =99651a(12) =279501a(13) =786071a(14) =2216437a(15) =6264663a(16) =17746897a(17) =50380895a(18) =143307269a(19) =408388819a(20) =1165819757a(21) =3333448075a(22) =9545909641a(23) =27375525727a(24) =78612676241a(25) =226034151539a(26) =650692800633