a(n) = 1^n + 6^n + 9^n.

Terms

a(0) =3a(1) =16a(2) =118a(3) =946a(4) =7858a(5) =66826a(6) =578098a(7) =5062906a(8) =44726338a(9) =397498186a(10) =3547250578a(11) =31743856666a(12) =284606318818