#663, September 13 - September 19, 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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Supporter Members have access to all these puzzles going back to number 1.
Discussion...
Post an idea here...
... by: Serban
# 663 A4=6 Basics to 23
@ Dieter thank you F9=H8=3 OR F9=G4=3 solve
1. Number 2 n=2 e=7 N=29 Nc=44 Ns=44 => B2=G7=2 solve
2. Number 5 n=2 e=7 N=26 Nc=25 Ns=14 =>
-- 2a. B7=5 basics to 50 => XY-Wing-379 [FH6,H8] => F8 <>7 = > F8=8 solve
--- 2b. A2=J3=5 solve
3. Number 9 n=2 e=7 N=28 Nc=33 Ns=3 => B1=J2=9 solve
Note : E4=H6=9
... by: Dieter
@Yves
For me "solves" means you can solve the puzzle with basic logic steps like single cells, hidden pairs, triplets, quadruplets, x-chain. No try and error needed anymore.
... by: Dieter
@Serban:
F9=H7=3 >> H7 is preset with 8
... by: Dieter
#663 - initially populated cells: 22 = 27,2%
No solver used.
basics: A4 = 6
populated cells: 23 = 28,4%
Strategy: Numbers 6,1,4,7 occur most frequently, combine two cells.
combinations of E5 = (1,6,8) and E7 = (3,4,7,9)
4 matrices left after basic checks: E5/E7 = 1/3, 8/3, 1/7 and 8/7
E5/E7 = 8/7 solve with C4=8
Review:
C4=8 & E7=7 solve.
... by: Serban
# 663 A4=6 Basics to 23
1. Number 3 n=2 e=7 N=24 Nc=14 Ns=14 => F9=H7=3 OR F9=G4=3solve
2. Column 4 n=3 e=6 Nc=18 Ns=4=> B4=7 & C4=8 solve
Note: D4=5 => F5=2
... by: Yves
B6=3 & B7=5 solve
I'm asking the community what the word "solve" means.
A puzzle is said to be solved when the successive steps leading to the solution are basic singletons (cells or groups).
Do you agree ?
