a(n) = 11^n - 7^n.

Terms

a(0) =0a(1) =4a(2) =72a(3) =988a(4) =12240a(5) =144244a(6) =1653912a(7) =18663628a(8) =208594080a(9) =2317594084a(10) =25654949352a(11) =283334343868