a(n) = 64*9^(n-2), a(0)=1, a(1)=7.

Terms

a(0) =1a(1) =7a(2) =64a(3) =576a(4) =5184a(5) =46656a(6) =419904a(7) =3779136a(8) =34012224a(9) =306110016a(10) =2754990144a(11) =24794911296a(12) =223154201664