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

Terms

a(0) =1a(1) =0a(2) =48a(3) =488a(4) =4064a(5) =32728a(6) =262096a(7) =2097096a(8) =16777152a(9) =134217656a(10) =1073741744a(11) =8589934504a(12) =68719476640a(13) =549755813784