a(n) = 8^n + 3^n - 1.

Terms

a(0) =1a(1) =10a(2) =72a(3) =538a(4) =4176a(5) =33010a(6) =262872a(7) =2099338a(8) =16783776a(9) =134237410a(10) =1073800872a(11) =8590111738a(12) =68720008176a(13) =549757408210