a(n) = 6^n - n^11.

Terms

a(0) =1a(1) =5a(2) =-2012a(3) =-176931a(4) =-4193008a(5) =-48820349a(6) =-362750400a(7) =-1977046807a(8) =-8588254976a(9) =-31370981913a(10) =-99939533824a(11) =-284948873555a(12) =-740831588352