'Generates a siret number (14 digits).
It is in fact the result of the concatenation of a siren number (9 digits),
a sequential number (4 digits) and a control number (1 digit) concatenation.
If $max_sequential_digits is invalid, it is set to 2.
:param max_sequential_digits The maximum number of digits for the sequential number (> 0 && <= 4).'

@classmethod
def siret(cls, max_sequential_digits=2):

    if ((max_sequential_digits > 4) or (max_sequential_digits <= 0)):
        max_sequential_digits = 2
    sequential_number = str(cls.random_number(max_sequential_digits)).zfill(4)
    return cls.numerify((((cls.siren() + u'    ') + sequential_number) + u'#'))
