a(n) = 5^n - n^11.

Terms

a(0) =1a(1) =4a(2) =-2023a(3) =-177022a(4) =-4193679a(5) =-48825000a(6) =-362781431a(7) =-1977248618a(8) =-8589543967a(9) =-31379106484a(10) =-99990234375a(11) =-285262842486a(12) =-742764230063