a(n) = 5^n - n^8.

Terms

a(0) =1a(1) =4a(2) =-231a(3) =-6436a(4) =-64911a(5) =-387500a(6) =-1663991a(7) =-5686676a(8) =-16386591a(9) =-41093596a(10) =-90234375a(11) =-165530756a(12) =-185841071a(13) =404972404a(14) =4627726569a(15) =27954687500a(16) =148292923329a(17) =755963695684