7^n + 5^n - 1.

Terms

a(0) =1a(1) =11a(2) =73a(3) =467a(4) =3025a(5) =19931a(6) =133273a(7) =901667a(8) =6155425a(9) =42306731a(10) =292240873a(11) =2026154867a(12) =14085427825a(13) =98109713531a(14) =684326588473