a(n) = 12^n - n^6.

Terms

a(0) =1a(1) =11a(2) =80a(3) =999a(4) =16640a(5) =233207a(6) =2939328a(7) =35714159a(8) =429719552a(9) =5159248911a(10) =61916364224a(11) =743006599127