def quadratic_nonresidue(self): """ Return a quadratic non-residue in ``self``. EXAMPLES:: sage: R = Integers(17) sage: R.quadratic_nonresidue() 3 sage: R(3).is_square() False """ try: return self._nonresidue except AttributeError: for a in self: if not a.is_square(): self._nonresidue = a return a