a(n) = 10^n - n^7.

Terms

a(0) =1a(1) =9a(2) =-28a(3) =-1187a(4) =-6384a(5) =21875a(6) =720064a(7) =9176457a(8) =97902848a(9) =995217031a(10) =9990000000a(11) =99980512829a(12) =999964168192