@staticmethod
def format_num(n):
    """
        Intelligent scientific notation (.3g).

        Parameters
        ----------
        n  : int or float or Numeric
            A Number.

        Returns
        -------
        out  : str
            Formatted number.
        """
    f = '{0:.3g}'.format(n).replace('+0', '+').replace('-0', '-')
    n = str(n)
    return f if len(f) < len(n) else n
