# Quadratic residue

We call an element
a
in the set $Z_n$ a **quadratic
residue** if for some
x
,

In the group $Z^{*}_p$, exactly half of
{1,...,p-1}
are **quadratic residues**.

In the group

Exactly half of

are quadratic residues.

External references

- Quadratic Residues, Ben Lynn