a(n) = 1^n + 7^n + 9^n.

Terms

a(0) =3a(1) =17a(2) =131a(3) =1073a(4) =8963a(5) =75857a(6) =649091a(7) =5606513a(8) =48811523a(9) =427774097a(10) =3769259651a(11) =33358386353a(12) =296270823683