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

Terms

a(0) =3a(1) =14a(2) =78a(3) =476a(4) =3042a(5) =19964a(6) =133338a(7) =901796a(8) =6155682a(9) =42307244a(10) =292241898a(11) =2026156916a(12) =14085431922a(13) =98109721724a(14) =684326604858