'), Function('r')

    >>> hyper_re(-f(x) + Derivative(f(x)), r, k)
    (k + 1)*r(k + 1) - r(k)
    >>> hyper_re(-x*f(x) + Derivative(f(x), (x, 2)), r, k)
    (k + 2)*(k + 3)*r(k + 3) - r(k)

    See Also
    ========

    sympy.series.formal.exp_re
    Nr*