(2*3^(n-1)+1)^2.

Terms

a(0) =9a(1) =49a(2) =361a(3) =3025a(4) =26569a(5) =237169a(6) =2128681a(7) =19140625a(8) =172213129a(9) =1549760689a(10) =13947373801a(11) =125524947025