Below is a very special grid, around each shaded number are 8 white squares.
However, each white square should have a number from 1 to 7.
Once filled in, these 8 numbers will sum to the shaded number.
In addition, once completed correctly, no row nor column will contain a duplicate number within a white square.
For example, the top row may be 5 6 4 2 3 1 7, etc.
This is a very difficult puzzle, and many people resort to using a computer to help them, which is a challenge in itself.
Puzzle Copyright © Kevin Stone
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Hint
This puzzle almost certainly requires trial-and-error to solve, and there is more than one solution.
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