A numeric mode is from one to  four  octal  digits  (0-7),
       derived  by  adding  up  the bits with values 4, 2, and 1.
       Any omitted digits are assumed to be leading  zeros.   The
       first  digit  selects the set user ID (4) and set group ID
       (2) and save text image [`sticky']  (1)  attributes.   The
       second digit selects permissions for the user who owns the
       file: read (4), write (2),  and  execute  (1);  the  third
       selects  permissions  for other users in the file's group,
       with the same values; and the fourth for other  users  not
       in the file's group, with the same values.