a(n) = 2*n + 7^n + 5^n.

Terms

a(0) =2a(1) =14a(2) =78a(3) =474a(4) =3034a(5) =19942a(6) =133286a(7) =901682a(8) =6155442a(9) =42306750a(10) =292240894a(11) =2026154890a(12) =14085427850a(13) =98109713558a(14) =684326588502