a(n) = (3*10^n - 6^n)/2.

Terms

a(0) =1a(1) =12a(2) =132a(3) =1392a(4) =14352a(5) =146112a(6) =1476672a(7) =14860032a(8) =149160192a(9) =1494961152a(10) =14969766912a(11) =149818601472