a(n) = 7^n + 9^n.

Terms

a(0) =2a(1) =16a(2) =130a(3) =1072a(4) =8962a(5) =75856a(6) =649090a(7) =5606512a(8) =48811522a(9) =427774096a(10) =3769259650a(11) =33358386352a(12) =296270823682