def create_block_data_string(string):
    """Create the required format for block data. The result is in the format:
    ``#<n><XX><string>`` where ``<XX>`` is the number of bytes following and
    ``<n>`` the length of <XX>

    Sample: #211abcdefghijk
    """
    return "#{}{}{}".format(len(str(len(string))), len(string), string)