#704, June 27 - July 3, 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: Dieter
#704 - initially populated cells: 21 = 25,9 %
No solver used, solver = brain.
basics: %
Strategy: numbers 1,6,8 occur most frequently, combine two cells with almost same candidates.
combinations of F6 = (1,6,8) and J6 = (1,2,3,5,8)
after basic checks 6 matrices left: 1/2, 1/5, 6/1, 8/1, 8/3 and 8/5
F6=8 & J6=1 solve with E6=6
Optimization:
E6=6 & J6=1 solve.
... by: Norman Powell
A few more eliminations through Forcing Networks otherwise unsolvable.
Read from bottom and rows numbered, columns lettered:
Forcing Networks Value 2 in Row 1 Column H cannot be ON so eliminate
Contradiction: No possibilities left for Row 1 Column D
Forcing Networks Value 2 in Row 1 Column E cannot be ON so eliminate
Contradiction: More than one Value 7 ON in Column G
Confined to Box Value 6 is confined to Column A and Box 1.
Forcing Networks Value 6 in Row 7 Column A cannot be ON so eliminate
Contradiction: More than one Value 4 ON in Row 7
Forcing Networks Value 4 in Row 1 Column G cannot be ON so eliminate
Contradiction: More than one Value 5 ON in Row 9
Forcing Networks Value 5 in Row 5 Column F cannot be ON so eliminate
Contradiction: More than one Value 4 ON in Box 4
Forcing Networks Value 4 in Row 5 Column A cannot be ON so eliminate
Contradiction: More than one Value 3 ON in Row 6
Forcing Networks Value 5 in Row 8 Column B cannot be ON so eliminate
Contradiction: More than one Value 5 ON in Column I
Hidden Singles In Column 9 I2 = 8.
Forcing Networks Value 8 in Row 8 Column I cannot be ON so eliminate
Contradiction: More than one Value 1 ON in Column I
Forcing Networks Value 4 in Row 9 Column G cannot be ON so eliminate
Contradiction: More than one Value 9 ON in Row 5
Hidden Pairs Hidden Pair in Box 6, for Values: 1 3 in Cells: I4 H6
... by: Serban
# 704 Basics to 21
1. A7=9 & C9=4 solve
2. D1=2 & F3=7 solve
3. A7=9 & F3=7 solve
