a(n) = 2^n + 4^n + 9^n.

Terms

a(0) =3a(1) =15a(2) =101a(3) =801a(4) =6833a(5) =60105a(6) =535601a(7) =4799481a(8) =43112513a(9) =387683145a(10) =3487834001a(11) =31385255961a(12) =282446317793