def prefixes(count_start=200, count=1000):
    """
    CO (Prefix) Rules:
    * Starts with [2-9].
    * Does not end with 11 (N11).
    """
    co = []

    for x in range(count_start, count):
        s = str(x)
        # N11
        if s[1:] == '11':
            continue
        co.append(x)

    return co