a(n) = 1^n + 3^n + 8^n.

Terms

a(0) =3a(1) =12a(2) =74a(3) =540a(4) =4178a(5) =33012a(6) =262874a(7) =2099340a(8) =16783778a(9) =134237412a(10) =1073800874a(11) =8590111740a(12) =68720008178a(13) =549757408212