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

Terms

a(0) =0a(1) =5a(2) =55a(3) =485a(4) =4015a(5) =32525a(6) =261415a(7) =2094965a(8) =16770655a(9) =134198045a(10) =1073682775a(11) =8589757445a(12) =68718945295a(13) =549754219565