a(n) = (5*9^n + 1)/2.

Terms

a(0) =3a(1) =23a(2) =203a(3) =1823a(4) =16403a(5) =147623a(6) =1328603a(7) =11957423a(8) =107616803a(9) =968551223a(10) =8716961003a(11) =78452649023a(12) =706073841203