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

Terms

a(0) =2a(1) =10a(2) =70a(3) =462a(4) =3018a(5) =19922a(6) =133262a(7) =901654a(8) =6155410a(9) =42306714a(10) =292240854a(11) =2026154846a(12) =14085427802a(13) =98109713506a(14) =684326588446