SUDOKU

Write a number from 1 to 9 into each empty square in the grid so that every number from 1 to 9 appears exactly once in each horizontal row, each vertical column, and each 3×3 block.
1  7      89  
  3          16
8      6      2
      8  3      
    6  7  5    
      9          
4      2      1
68            5
  51      23  
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