def E_CMFR_N(t, N):
    """Calculate a dimensionless measure of the output tracer concentration
    from a spike input to a series of completely mixed flow reactors.

    :param t: The time(s) at which to calculate the effluent concentration. Time can be made dimensionless by dividing by the residence time of the CMFR.
    :type t: float or numpy.array
    :param N: The number of completely mixed flow reactors (CMFRS) in series. Must be greater than 1.
    :type N: int

    :return: Dimensionless measure of the output tracer concentration (concentration * volume of 1 CMFR) / (mass of tracer)
    :rtype: float

    :Examples:

    >>> from aguaclara.research.environmental_processes_analysis import E_CMFR_N
    >>> round(E_CMFR_N(0.5, 3), 7)
    0.7530643
    >>> round(E_CMFR_N(0.1, 1), 7)
    0.9048374
    """
    return (N**N)/special.gamma(N) * (t**(N-1))*np.exp(-N*t)