Examples
        ========

        >>> from sympy.algebras.quaternion import Quaternion
        >>> q = Quaternion(2, 4, 2, 4)
        >>> q.index_vector()
        0 + 4*sqrt(10)/3*i + 2*sqrt(10)/3*j + 4*sqrt(10)/3*k

        See Also
        ========

        axis
        norm

        N)