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

Terms

a(0) =1a(1) =7a(2) =-64a(3) =-1675a(4) =-12288a(5) =-45357a(6) =-17792a(7) =1273609a(8) =14680064a(9) =129434759a(10) =1063741824a(11) =8570447421a(12) =68683644928a(13) =549693065371