   ,         ,   
  9.      ,  , 
     ,    
  1,2,3,4,5,6,7,8,0,1,2,3,4,5,6,7,8,0,1,2,3 ...

     . ,        
,          10**k-1 
( -  ),    9 (   
  , ..  ).   ,   
   ,      9,  
       ,   
1,2,3,4,5,6,7,8,0,1,2,3,4,5,6,7,8,0,1,2,3 ...
..       :)   :   
  9   1, ..        1 
.

    .