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#698, May 16 - May 22, 2026:
The Weekly 'Unsolvable' Sudoku Puzzle

by Klaus Brenner, guest compiler
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).

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.
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Supporter Members have access to all these puzzles going back to number 1.

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Saturday 16-May-2026

... by: Frans Goosens

#698

Combination 2-digits cells

C5=1 No solution, Undo calculation
C5=6 Wrong, Undo calculation
C5=1 No solution, Fixed
C4=2 ( G5=3 ) Solved,

Total solving time is : 27 sec.
Number of logical steps is : 3163

Saturday 16-May-2026

... by: Dieter

#698 - initially populated cells: 25 = 30,9 %
No solver used, solver = brain.
basics: J1=9
populated cells: 26 = 32,1 %

Strategy: numbers 9,1,3,4,7 occur most frequently, combine two cells with almost same candidates.
combinations of D5 = (3,4,6,7,9) and D6 = (4,5,6,7)
after basic checks 5 matrices left: D5/D6 = 4/6, 6/4, 7/6, 9/4, 9/6
D5/D6 = 9/4 solves with E4=5

Optimization:
D6=4 & E4=5 solve.

Saturday 16-May-2026

... by: Serban

# 698 J1=9 Basics to 26

1. F4=H2=3 solve

2. A3=F5=6 solve

Saturday 16-May-2026

... by: Serban

# 698 J1=9 Basics to 26

1. J8=4 solve

2. B2=E4=5 solve

3. J6=7 solve

Saturday 16-May-2026

... by: Yves

J7=3 & A7=2

A7=2 & D2=6

D2=6 & J7=3

... etc ...
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