def convert_base(n, b):
    """
    convert_base(integer, integer) -> string
 
    Return the textual representation of n (decimal) in base 2 <= b <= 36.
    """

    assert 2 <= b <= 36
    
    result = ""

    if n == 0:
        return "0"

    digits = "0123456789abcdefghijklmnopqrstuvwxyz"
        
    while n != 0:
        digit = n%b
        n = n//b
        #result = str(digit) + result
        result = digits[digit] + result

    return result