a(n) = 4^n + 5^n + 8^n.

Terms

a(0) =3a(1) =17a(2) =105a(3) =701a(4) =4977a(5) =36917a(6) =281865a(7) =2191661a(8) =17233377a(9) =136432997a(10) =1084556025a(11) =8642957021a(12) =68980394577a(13) =551043625877