a(n) = 4^n + 6^n + 7^n.

Terms

a(0) =3a(1) =17a(2) =101a(3) =623a(4) =3953a(5) =25607a(6) =168401a(7) =1119863a(8) =7509953a(9) =50693447a(10) =343990001a(11) =2344318103a(12) =16034846753a(13) =110016813287a(14) =756855672401