a(n) = 9^n - n^11.

Terms

a(0) =1a(1) =8a(2) =-1967a(3) =-176418a(4) =-4187743a(5) =-48769076a(6) =-362265615a(7) =-1972543774a(8) =-8546887871a(9) =-30993639120a(10) =-96513215599a(11) =-253930611002a(12) =-460578834207a(13) =749705434292