#713, August 29 - September 4, 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.
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Supporter Members have access to all these puzzles going back to number 1.
Discussion...
Post an idea here...
... by: Norman Powell
Requires 1 Bowman's Bingo to Solve, long solution path, opening similar to AS's but different methods used due to different order of methods:
Hidden Single in Row C, C6=3. [As AS]
Hidden Pair Box 7, Values 3, 4 in Cells H1, J3, eliminate 2, 7 from H1 and 2 from J3. [As AS]
Finned X-Wing: FH19 with Fin F3 for Value 3, eliminate 3 from D1 & E1. [AS uses 2 x Grouped X-Cycles for the same eliminations. For me Finned X-Wing is a simpler and quicker pattern to find than Grouped X-Cycles, so I deploy earlier].
Alternating Inference Chains: Value 8 of Cell A7 has weak links to Chain eliminate. [AS finds this part of Forcing Networks Elimination Setting A7=4, which I do not pick up until later. I have AIC earlier than FN as less powerful, but the searches are longer]
Forcing Networks 1st Pass: Eliminate 4A3, 2A7, 6A7, [last two as AS FN A7=4], 4B8, 9D5 [As AS FN, AS's last elimination], 4D7.
Bowman's Bingo: 6 Trial values over 4 levels of eliminates 4D6, Solving D6=9.
Forcing Networks 2nd Pass: Eliminate 2B1, 6C7, 2D7, 6F6, 2G3, 6G8, 2H2, 2J4.
Hidden Pair in Box 7 for Values 2 &5 in Cells G1 &J2, eliminate other possibilities in those Cells.
Almost Locked Sets: Set 1 F6, H6 for values 2, 4, 5, Set 2 D8, F8, G8 for values 2, 4, 5, 7 with restricted value 5
Rule 1: Eliminate all possibilities that can see non-restricted commons in both ALSs: 2H8.
Alternating Inference Chains: 6 J5 has weak links to both ends of a chain eliminate.
Forcing Networks 3rd Pass: Eliminate 2A2, 7A2, 2, A6, then finds a solution.
... by: Frans Goosens
#713
Combination 2-digits cells
D6=4 Wrong, Undo calculation
D6=9 No solution, Fixed
E7=2 No solution, Undo calculation
E7=3 No solution, Undo calculation
H1=3 No solution, Undo calculation
H1=4 Wrong, Undo calculation
H1=3 No solution, Fixed
B3=2 No solution, Undo calculation
B3=9 No solution, Undo calculation
D1=2 No solution, Undo calculation
D1=7 No solution, Undo calculation
E7=2 ( D1=7 ) Solved,
Total solving time is : 71 sec.
Number of logical steps is : 10107
... by: Dieter
#713 - initially populated cells: 22 = 27,2 %
No solver used, solver = brain.
basics: C6=3; H1/J3 =3/4 or 4/3
populated cells: 23 = 28,4 %
Strategy: numbers 3,1,4,8,9 occur most frequently, combine two cells with almost same candidates.
combinations of H2 = (1,2,7) and H9 = (2,3,7,8,9);
after basic checks 3 matrices left: 7/2, 7/3 and 7/8
H2=7 & H9=8 solve with H6=2.
Optimization:
H6=2 & H9=8 solve.
... by: Serban
# 713 C6=3 Basics to 23
1. H9=8 & J9=2 solve
2. D8=4 & F9=3 solve
3. C7=8 & F9=3 solve
4. C9=9 & F9=3 solve
5. C7=8 & any[ A2,F3,D4]=8 solve
