#680, January 10 - January 16, 2026:
The Weekly 'Unsolvable' Sudoku Puzzle
by Andrew Stuart
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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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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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Discussion...
Post an idea here...
... by: Dieter
#680 - initially populated cells: 24 = 29,6 %
No solver used, solver = brain.
basics: A8=5; G7=6; C2=2; F8=8
populated cells: 28 = 34,6 %
Strategy: numbers 5,2,6,8,7 occur most frequently, combine two cells.
combinations of C3 = (1,5,8) and C9 = (3,4,8)
C3/C9 = 5/3 solves.
Optimization:
C9=3 solves.
... by: Frans Goosens
#680
A7=2 Wrong, Undo calculation
A7=4 ( B7=2 ) Solved,
Total solving time is : 5 sec.
Number of logical steps is : 335
... by: Yves
E3=4 Or J5=3
... by: Serban
# 680 A8=5 C2=2 F8=8 G7=6 Basics 28
1.Column 7 n=5 e=4 Nc=4 Ns=2 => H7=3 OR B7=2 solve
2. Number 3 n=2 e=7 N=27 Nc=16 Ns=9 => H7=3 OR C9=3 solve
