#707, July 18 - July 24, 2026:
The Weekly 'Unsolvable' Sudoku Puzzle
by Richard Kröger, guest compiler
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WARNING: This is the Weekly 'Unsolvable' Sudoku, rated above 'Extreme'.
This is currently unsolvable by my solver, except perhaps with trial and error strategies.
Using the solver will not help you. (much).
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Changes March 2026
Due to the introduction of
Forcing Nets many Weekly Unsolvable puzzles can now
be solved. I have flagged all the Sudoku ones which are solvable. I am struggling to make any new ones so we'll
have to see if the Weekly can continue. The point of the Weekly was to provoke discussion and new ideas, so
that is progress. But my solution is unlikely to be optimal so alternatives are welcome.
Archive
Each week a new 'unsolvable' will be published and the previous will be accessible here from this archive section.
If you like very tough puzzles, these are for you.
Share and Enjoy
Supporter Members have access to all these puzzles going back to number 1.
Discussion...
Post an idea here...
... by: Frans Goosens
#707
With trial and error
Combination A2=456 and I9=345
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A2=4 I9=3 Wrong, Undo calculation
All reset to initial position
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A2=4 I9=4 Wrong, Undo calculation
All reset to initial position
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A2=4 I9=5 Wrong, Undo calculation
All reset to initial position
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A2=5 I9=3 Wrong, Undo calculation
All reset to initial position
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A2=5 I9=4 Wrong, Undo calculation
All reset to initial position
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A2=5 I9=5 Wrong, Undo calculation
All reset to initial position
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A2=6 I9=3 Wrong, Undo calculation
All reset to initial position
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A2=6 I9=4 ( C7=3 ) Solved,
Total solving time is : 105 sec.
Number of logical steps is : 14090
... by: Norman Powell
This is solvable with your solver.
Here is my solution path as an alternative (Rows numbered, Columns lettered, read from the bottom up),
Forcing Networks do the heavy lifting:
Solved Cells and Hidden Singles mop up.
XY-Cycles Value 3 of Cell G5 can see both ends of Chain - Eliminate
Rectangular Elimination Value 1 ON in Cell E6 and Strong Link E2 A2 would eliminate all 1s from Box 4 - so Eliminate
Hidden Pairs Hidden Pair in Box 6, for Values: 3 6 in Cells: I4 G5
X-Wing FH18 for Value 3
Hidden Singles In Box 3 I3 = 9.
In Column 6 F2 = 9.
Hidden Pairs Hidden Pair in Row 8, for Values: 3 5 in Cells: F8 H8
Hidden Singles In Box 9 G8 = 1.
In Column 7 G9 = 7.
WXYZ-Wing Hinge H8 Corners G8 H5 G9 Constrained Values 3 5 1
Eliminate Unconstrained Value 7 from Cells: H7 G6
Y-Wing Hinge H5 Corners C5 H8 Constrained Values 5 7
Eliminate Unconstrained Value 3 from Cells: C8
Alt. Inf. Chains Value 3 of Cell H5 has weak links to both ends of the chain
This possibility would cause a contradiction - Eliminate
WXYZ-Wing Hinge C6 Corners B6 C1 B4 Constrained Values 1 9 7
Eliminate Unconstrained Value 4 from Cells: C5
Hidden Singles In Row 1 G1 = 5.
X-Wing FH58 for Value 5
Hidden Singles In Column 2 B8 = 2.
Solved Cells Cell B1 = 6
Forcing Networks Value 5 in Row 8 Column G cannot be ON so eliminate
Contradiction: No possibilities left for Row 9 Column E
Value 6 in Row 8 Column B cannot be ON so eliminate
Contradiction: More than one Value 2 ON in Row 4
Value 7 in Row 6 Column C cannot be ON so eliminate
Contradiction: No possibilities left for Row 7 Column E
Value 2 in Row 6 Column B cannot be ON so eliminate
Contradiction: More than one Value ON in Row 4 Column A
Value 2 in Row 5 Column H cannot be ON so eliminate
Contradiction: More than one Value 4 ON in Column I
Value 5 in Row 5 Column G cannot be ON so eliminate
Contradiction: More than one Value 2 ON in Column A
Value 2 in Row 5 Column G cannot be ON so eliminate
Contradiction: More than one Value 5 ON in Column H
Value 2 in Row 4 Column B cannot be ON so eliminate
Contradiction: No possibilities left for Value 5 in Row 8
Value 5 in Row 3 Column G cannot be ON so eliminate
Contradiction: More than one Value 2 ON in Row 4
Value 6 in Row 1 Column C cannot be ON so eliminate
Contradiction: More than one Value 2 ON in Row 4
Value 6 in Row 1 Column B cannot be OFF so eliminate other values
Contradiction: More than one Value 2 ON in Row 4
Value 5 in Row 1 Column B cannot be ON so eliminate
Contradiction: More than one Value 2 ON in Row 4
Value 4 in Row 1 Column B cannot be ON so eliminate
Contradiction: More than one Value 2 ON in Row 4
Grouped Alt. Inf. Chains Value 7 of Cell G5 has weak links to both ends of the chain
This possibility would cause a contradiction - Eliminate
Forcing Networks Value 8 in Row 7 Column A cannot be ON so eliminate
Contradiction: More than one Value 2 ON in Row 6
Value 7 in Row 4 Column E cannot be ON so eliminate
Contradiction: No possibilities left for Row 1 Column F
Value 2 in Row 2 Column I cannot be ON so eliminate
Contradiction: More than one Value ON in Row 1 Column B
Value 1 in Row 2 Column C cannot be ON so eliminate
Contradiction: No possibilities left for Value 8 in Column C
Forcing Networks Value 5 in Row 9 Column G cannot be ON so eliminate
Contradiction: No possibilities left for Value 2 in Row 1
Value 5 in Row 7 Column H cannot be ON so eliminate
Contradiction: No possibilities left for Value 2 in Row 5
Value 9 in Row 2 Column I cannot be ON so eliminate
Contradiction: No possibilities left for Value 1 in Row 6
Value 7 in Row 2 Column F cannot be ON so eliminate
Contradiction: More than one Value 2 ON in Column A
Forcing Networks Value 5 in Row 3 Column I cannot be ON so eliminate
Contradiction: More than one Value 6 ON in Row 2
Forcing Networks Value 9 in Row 8 Column B cannot be ON so eliminate
Contradiction: More than one Value ON in Row 2 Column C
Value 6 in Row 2 Column C cannot be ON so eliminate
Contradiction: More than one Value 5 ON in Box 5
Value 6 in Row 1 Column G cannot be ON so eliminate
Contradiction: More than one Value 5 ON in Box 5
... by: Serban
# 707 Basics to 22
1. B1=4 & C2=5 solve
2. B5=1 & C4=4 solve
3. A7=5 & A8=4 solve
4. G8=2 & G9=5 solve
5. E4=7 & E8=5 solve
6. D5=2 & J5=3 solve
7. B7=G8=2 solve
8. G1=H8=3 solve
9. B1=G3=4 solve
10. E4=F8=7 solve
