#668, October 18 - October 24, 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: Serban
# 668 G7=8 Basics to 22
1. Number 2 n=2 e=7 N=30 Nc=67 Ns=61 => A5=J1=2 solve Nx=9
2. Number 2 n=2 e=7 N=30 Nc=67 Ns=61 => B2=2 basics to 39
1a.X chain x=4 =>[E6,DJ8,H59] <>4 => [D5 OR H8]=4 H5=7 J8=3 solve
3.B2=2 & any[J3,B4,C9,G5]=1 solve
4.B2=2 & any[A5,F6,C7,D9]=2 solve
4.B2=2 &any[G2,D4,B5,J8,E9]=3 solve
5.B2=2 & any[D5,J6,H8,E7,B9]=4 solve
6.B2=2 & any[A6,B7,D8,F1]=5 solve
7.B2=2 & G6=6 solve
8.B2=2 & any[G9,H5,J2]=7 solve
9.B2=2 & [E4 OR B6]=8
10.B2=2 & H9=9 solve
... by: BGH
Basics 27.2 (NEW 4 Step Solution #668)
4 @ H8 29.6 Cell Pair, one digit in solution
8 @ C8 35.8 Cell Pair, one digit in solution if this is a solution path
5 @ D8 49.4 Cell Pair, one digit in solution if this is a solution path
2 @ B2 Solution
Cell Pair,
Block 1x1 Unit Pair,
Column 1 Unit Pair
Dieter’ solution matches mine
... by: Dieter
#668 - initially populated cells: 21 = 25,9%
No solver used.
basics: G7=8
populated cells: 22= 27,2%
Strategy: Numbers 8,1,5 occur most frequently, combine two cells.
combinations of B2 = (2,3,4,8) and D8 = (3,4,5)
B2=2 & D8=5 solve.
... by: Frans Goosens
#668
With trial and error
Combination B1=239 and I8=349
************************************************************
B1=2 I8=3 Wrong, Undo calculation
All reset to initial position
************************************************************
B1=2 I8=4 Wrong, Undo calculation
All reset to initial position
************************************************************
B1=2 I8=9 Wrong, Undo calculation
All reset to initial position
************************************************************
B1=3 I8=3 Wrong, Undo calculation
All reset to initial position
************************************************************
B1=3 I8=4 Wrong, Undo calculation
All reset to initial position
************************************************************
B1=3 I8=9 Wrong, Undo calculation
All reset to initial position
************************************************************
B1=9 I8=3 No solution, Fixed
Combination 2-digits cells
A3=7 No solution, Undo calculation
A3=8 Wrong, Undo calculation
A3=7 No solution, Fixed
A2=2 Wrong, Undo calculation
A2=8 ( C1=3 ) Solved,
Total solving time is : 178 sec.
Number of logical steps is : 22411
... by: BGH
5 Step Solution to # 668
Basics 27.2
4 @ H8 29.6 Cell pair, one digit will be in the solution.
8 @ C8 35.8 Cell pair, one digit will be in the solution if this is a solution path.
5 @ D8 49.4 Cell pair, one digit will be in the solution if this is a solution path.
8 @ B6 56.8 Cell pair, one digit will be in the solution if this is a solution path.
7 @ D7 Solution. Cell pair, one digit will be in the solution if this is a solution path.
I could not find a unit pair that led to a solution.
... by: Serban
# 668 G7=8 Basics to 22
1. Number 9 n=2 e=7 N=27 Nc=34 Ns=7 => H9=9 basics to 43
1a. X chain x=6 =>[J1,F2,D4,H5,C9] <>6 => D1=6 solve
2. H9=9 & B4=1 solve
3. H9=9 & J1=2 solve
4. H9=9 & D4=3 solve
5. H9=9 & B9=4 solve
6. H9=9 & G6=6 solve
7. H9=9 & D7=7 solve
8. H9=9 & E4=8 solve
9. H9=9 & E6=9 solve
