a(n) = 7^n - n^8.

Terms

a(0) =1a(1) =6a(2) =-207a(3) =-6218a(4) =-63135a(5) =-373818a(6) =-1561967a(7) =-4941258a(8) =-11012415a(9) =-2693114a(10) =182475249a(11) =1762967862a(12) =13411305505a(13) =96073279686a(14) =676747283793