Group Sum Sudoku
A standard Sudoku, except that numbers in circles are equal to the sum of the digits in the four surrounding cells. As with other Sudoku variants, this additional rule creates a slightly different solving experience.
Place a digit from 1 to 9 in each empty cell so that each row, each column and each 3x3 block contains all the digits from 1 to 9. In addition, the number in each circle is equal to the sum of the digits in the four surrounding cells.
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