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

Terms

a(0) =1a(1) =5a(2) =-28a(3) =-513a(4) =-2800a(5) =-7849a(6) =0a(7) =162287a(8) =1417472a(9) =9546255a(10) =59466176a(11) =361025495a(12) =2173796352a(13) =13055867207a(14) =78356634560a(15) =470173593951