a(n) = 8^n - n^9.

Terms

a(0) =1a(1) =7a(2) =-448a(3) =-19171a(4) =-258048a(5) =-1920357a(6) =-9815552a(7) =-38256455a(8) =-117440512a(9) =-253202761a(10) =73741824a(11) =6231986901a(12) =63559696384a(13) =539151314515