WITH ctebins 
     AS (SELECT num AS num_orig, 
                num  AS working_level, 
                Cast('' AS VARCHAR(max)) AS binval 
         FROM   nums_bin 
         UNION ALL 
         SELECT c.num_orig, 
                c.working_level / 2, 
                Cast(c.working_level % 2 AS VARCHAR(max)) 
                + c.binval 
         FROM   ctebins c 
         WHERE  c.working_level > 0) 
SELECT num_orig, 
       binval 
FROM ctebins 
WHERE working_level = 0;