1^n + 4^n + 8^n.

Terms

a(0) =3a(1) =13a(2) =81a(3) =577a(4) =4353a(5) =33793a(6) =266241a(7) =2113537a(8) =16842753a(9) =134479873a(10) =1074790401a(11) =8594128897a(12) =68736253953a(13) =549822922753