def utility_num2columnletters(num):
    """
    Takes a column number and converts it to the equivalent excel column letters

    :param int num: column number
    :return str: excel column letters
    """

    def pre_num2alpha(num):
        if num % 26 != 0:
            num = [num // 26, num % 26]
        else:
            num = [(num - 1) // 26, 26]

        if num[0] > 26:
            num = pre_num2alpha(num[0]) + [num[1]]
        else:
            num = list(filter(lambda x: False if x == 0 else True, num))

        return num

    return "".join(list(map(lambda x: chr(x + 64), pre_num2alpha(num))))