a(n) = 8^n + 6^n - 1.

Terms

a(0) =1a(1) =13a(2) =99a(3) =727a(4) =5391a(5) =40543a(6) =308799a(7) =2377087a(8) =18456831a(9) =144295423a(10) =1134207999a(11) =8952731647a(12) =70896259071a(13) =562816507903