#659, August 16 - August 22, 2025:
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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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
#659 - initially populated cells: 23 = 28,4%
No solver used.
basics: %
Strategy: Numbers 1,4,5,6,9 occur most frequently, combine two cells.
combinations of F1 = (5,6,7,9) and G2 = (1,4,7,9)
4 matrices remain after basic checks: F1/G2 = 5/4, 6/4, 7/4 and 9/9
F1/G2 = 9/9 solves with E3=7
Review:
E3=7 & G2=9 solve.
... by: Frans Goosens
#659
With trial and error
Combination A5=239 and I8=358
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A5=2 I8=3 Wrong, Undo calculation
All reset to initial position
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A5=2 I8=5 Wrong, Undo calculation
All reset to initial position
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A5=2 I8=8 Wrong, Undo calculation
All reset to initial position
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A5=3 I8=3 Wrong, Undo calculation
All reset to initial position
************************************************************
A5=3 I8=5 Wrong, Undo calculation
All reset to initial position
************************************************************
A5=3 I8=8 Wrong, Undo calculation
All reset to initial position
************************************************************
A5=9 I8=3 Wrong, Undo calculation
All reset to initial position
************************************************************
A5=9 I8=5 No solution, Fixed
Combination 2-digits cells
B5=1 No solution, Undo calculation
B5=2 Wrong, Undo calculation
B5=1 No solution, Fixed
B6=2 Wrong, Undo calculation
B6=8 No solution, Fixed
B8=2 Wrong, Undo calculation
B8=4 ( I2=7 ) Solved,
Total solving time is : 155 sec.
Number of logical steps is : 19181
... by: Serban
# 659 Basics to 23
1.Row D n=3 e=6 Nc=29 Ns=19 => D5=7 & D7=8 solve
Note: D2=2 D9=1
2. Column 2 n=3 e=6 Nc=20 Ns=17 => A2=4 & C2=1 solve
... by: Dieter
#659 - initially populated cells: 23 = 28,4%
No solver used.
basics: %
Strategy: Numbers 1,4,5,6,9 occur most frequently, combine two cells.
combinations of E7 = (1,4,7,9) and J7 = (1,5,6,8)
3 matrices remain after basic checks: E7/J7 = 1/6, 4/6 and 7/6 > J7=6
E7/J7 = 4/6 solves with F2=8 & G3=4
Review:
F2=8 & G3=4 solve.
... by: Serban
# 659 Basics to 23
1. Box 3 GHJ123 n=3 e=6 Nc=34 Ns=30 => G2=9 & H3=3 solve
Note: H1=5 J1=1 J2=7
2. Box 4 ABC456 n=3 e=6 Nc=38 Ns=2 => A4=3 & C6=2 solve
Note: A5=9 B5=1
3. Number 3 n=2 e=7 N=30 Nc=76 Ns=28 => C1=G9=3 OR G9=J5=3 solve
