def _potInt(x,y,z,a2,b2,c2,n):
    """Integral involed in the potential at (x,y,z)
    integrates 1/A B^(n+1) where
    A = sqrt((tau+a)(tau+b)(tau+c)) and B = (1-x^2/(tau+a)-y^2/(tau+b)-z^2/(tau+c))
    from lambda to infty with respect to tau.
    The lower limit lambda is given by lowerlim function.
    """
    def integrand(tau):
        return _FracInt(x, y, z, a2, b2, c2, tau, n+1)
    return integrate.quad(integrand, lowerlim(x**2,y**2,z**2,a2,b2,c2), np.inf)[0]