def formation_factor(arch_a, phi, arch_m):
    """
    Computes Archie Formation Factor (F)

    Parameters
    ----------
    arch_a : float
        Archie Tortuosity Factor - a
    phi : [type]
        Porosity (decimal)
    arch_m : float
        Archie Cementation Exponent - m

    Returns
    -------
    float
        Returns Archie Formation Factor
    """
    return arch_a / phi ** arch_m