#691, March 28 - April 3, 2026:
The Weekly 'Unsolvable' Sudoku Puzzle
by Lars Rocha, 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
#691 - initially populated cells: 23 = 28,4 %
No solver used, solver = brain.
basics: G4=1
populated cells: 24 = 29,6 %
Strategy: numbers 1,7,2,8 occur most frequently, combine two cells.
combinations of D9 = (1,4,6,8) and F8 = (4,7,8,9)
after basic checks 7 matrices left: start with D9/F8 = 6/9 as it is most populated.
D9/F8 = 6/9 solves with B8=4.
Optimization:
B8=4 & D9=6 solve.
... by: Serban
# 691 Basics to 24
1. G3=J8=3 solve
2. B8=E9=4 solve
3. D9=J1=6 solve
... by: osiguy
Absolutely diabolical Andrew! I must place two answers first
# 1 R4C3=2 [D2B]
# 2 R4C5=3 [D2B]
Once i place these, then using expert approved techniques the board no longer stalls in the solver! Does anyone have any other placements as the first two that can open up for a full solver path!
Diabolical!
