a(n) = 1 - n^12.

Terms

a(0) =1a(1) =0a(2) =-4095a(3) =-531440a(4) =-16777215a(5) =-244140624a(6) =-2176782335a(7) =-13841287200a(8) =-68719476735a(9) =-282429536480a(10) =-999999999999