a(n) = 2^n + 3^n + 7^n.

Terms

a(0) =3a(1) =12a(2) =62a(3) =378a(4) =2498a(5) =17082a(6) =118442a(7) =825858a(8) =5771618a(9) =40373802a(10) =282535322a(11) =1977505938a(12) =13841822738a(13) =96890612922a(14) =678227872202