a(n) = 2*9^n+1.

Terms

a(0) =3a(1) =19a(2) =163a(3) =1459a(4) =13123a(5) =118099a(6) =1062883a(7) =9565939a(8) =86093443a(9) =774840979a(10) =6973568803a(11) =62762119219a(12) =564859072963