a(n) = 7^n + 5^n - 3^n + 2^n.

Terms

a(0) =2a(1) =11a(2) =69a(3) =449a(4) =2961a(5) =19721a(6) =132609a(7) =899609a(8) =6149121a(9) =42287561a(10) =292182849a(11) =2025979769a(12) =14084900481a(13) =98108127401a(14) =684321821889