a(n) = 3^n + 4^n + 8^n.

Terms

a(0) =3a(1) =15a(2) =89a(3) =603a(4) =4433a(5) =34035a(6) =266969a(7) =2115723a(8) =16849313a(9) =134499555a(10) =1074849449a(11) =8594306043a(12) =68736785393a(13) =549824517075