a(n) = 1^n + 5^n + 8^n.

Terms

a(0) =3a(1) =14a(2) =90a(3) =638a(4) =4722a(5) =35894a(6) =277770a(7) =2175278a(8) =17167842a(9) =136170854a(10) =1083507450a(11) =8638762718a(12) =68963617362a(13) =550976517014