#710, August 8 - August 14, 2026:
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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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.
Share and Enjoy
Supporter Members have access to all these puzzles going back to number 1.
Discussion...
Post an idea here...
... by: Norman Powell
Forcing Networks achieves an additional elimination to AS's solver: 1 in F9, which AS picks up as a pointing pair anyway.
Bowman's Bingo Eliminates 3 from F9 after 21 guesses over 5 levels, which solves F9 as 6.
No other techniques make a mark until:
The second pass of Forcing Networks, after identify 12 eliminations then solves the grid when testing Value 5 H9.
... by: Dieter
#710 - initially populated cells: 23 = 28,4 %
No solver used, solver = brain.
basics: %
Strategy: numbers 1,2,4,7,8 occur most frequently, combine two cells with almost same candidates.
combinations of H2 = (1,2,5,8,9) and H1 = (1,2,7,8);
after basic checks 7 matrices left: 1/2, 1/7, 1/8, 5/1, 8/1, 8/2 and 9/1;
H2=8 & H1=2 solve with J1=4.
Optimization:
H1=2 & J1=4 solve.
... by: Serban
# 710 Basics to 23
1. C1=F2=1 OR C1=J3=1 OR F2=J3=1 solve
2. G2 =H9 =5 solve
3. J3 =1 & J8=8 solve
4. E7=2 & J8=8 solve
5. H4=1 & H5=9 solve
6. E1=6 & F2=1 solve
