I really don't know what you mean by "defining a Legendre symbol", but since , we obtain by the multiplicativity of the Legendre symbol and by the quadratic reciprocity theorem . Now:

**

Tonio

** , and then is the product of a quadratic residue (9) and a non-quadratic residue (3), and thus it itself is a

non-quad. res., so

In short, 135 is the product of two non-quad. res. and thus it is a quad. residue. After some calculation,