a(n) = 10^n - n^12.

Terms

a(0) =1a(1) =9a(2) =-3996a(3) =-530441a(4) =-16767216a(5) =-244040625a(6) =-2175782336a(7) =-13831287201a(8) =-68619476736a(9) =-281429536481a(10) =-990000000000