a(n) = 3^n + 5^n + 9^n.

Terms

a(0) =3a(1) =17a(2) =115a(3) =881a(4) =7267a(5) =62417a(6) =547795a(7) =4863281a(8) =43443907a(9) =389393297a(10) =3496609075a(11) =31430064881a(12) =282674208547