a(n) = 2^n + 6^n + 9^n.

Terms

a(0) =3a(1) =17a(2) =121a(3) =953a(4) =7873a(5) =66857a(6) =578161a(7) =5063033a(8) =44726593a(9) =397498697a(10) =3547251601a(11) =31743858713a(12) =284606322913