a(n) = 3^(n-1)*(6*3^(n-1) + 5) + 1.

Terms

a(0) =12a(1) =70a(2) =532a(3) =4510a(4) =39772a(5) =355510a(6) =3192292a(7) =28708750a(8) =258313132a(9) =2324621350a(10) =20921001652a(11) =188287243390