a(n) = 3^n + 4^n + 7^n.

Terms

a(0) =3a(1) =14a(2) =74a(3) =434a(4) =2738a(5) =18074a(6) =122474a(7) =842114a(8) =5836898a(9) =40635434a(10) =283582874a(11) =1981698194a(12) =13858595858a(13) =96957713594a(14) =678496291274