def multiple(a, b):
    """Return the smallest number n that is a multiple of both a and b.

    >>> multiple(3, 4)
    12
    >>> multiple(14, 21)
    42
    """
    "*** YOUR CODE HERE ***"
    i = 2
    while i <= min(a, b):
        if (a % i == 0) and  (b % i == 0):
            return i * multiple(a // i, b // i)
        else:
            i += 1
    return a * b


def unique_digits(n):
    """Return the number of unique digits in positive integer n

    >>> unique_digits(8675309) # All are unique
    7
    >>> unique_digits(1313131) # 1 and 3
    2
    >>> unique_digits(13173131) # 1, 3, and 7
    3
    >>> unique_digits(10000) # 0 and 1
    2
    >>> unique_digits(101) # 0 and 1
    2
    >>> unique_digits(10) # 0 and 1
    2
    """
    "*** YOUR CODE HERE ***"
    return len(set(str(n)))
