Dutch Flat Mates: Friendly Sums
(Published on 19. November 2025, 07:00 by Flinty)
Special Thanks
Inspiration for this puzzle comes from The Quaker's Quiver by mathpesto.
Previous Dutch Flat Mate Puzzles
This has been a weekly series since '18 Oct 23'. Here is a spreadsheet link for all the previous puzzles in the series, which also has a few teasers for upcoming constraints/guest setters in the series (subject to change).
This alternative link offers a limited LMD search for Dutch Flat Mates.
To play the puzzle, please click the image:
Puzzle Link: Click Here
Initial Setter Difficulty: 2.5-3 / 5
Normal Sudoku rules apply
Place the digits 1-9 so that they do not repeat in any row, column, or 3x3 box.
Dutch Flats
Every 5 in the grid must have a '1' directly above it or a '9' directly below it. It may have both, but it doesn't need both.
Friendly Sums
A digit in a cell with arrows equals the total sum of all digits in "friendly cells" in those directions.
A cell is "friendly" if its digit is equal to the cell's Row, Column, and/or Box number.
Hint to start
It's not really a 'negative constraint', but not busting the sum is crucial throughout the solve, and any time you're stuck this is definitely worth reconsidering. R5C5 is the intended first digit.
Guest Setter
Next week we have another debutant to the series, and you'll have a great time getting all snuggled up with Allagem!
Solution code: Row 7 Digits
Comments
on 20. November 2025, 05:21 by therealsillypenguin
Really cool puzzle! I will have to check the inspiration puzzle out, because the friendly sums were such an interesting rule I had never seen before
on 19. November 2025, 19:26 by mathpesto
Happy to have inspired this gem of a puzzle! The flatmates rule does a lot of cool stuff here :)
on 19. November 2025, 17:34 by marcmees
Great contribution to the series. Thanks
on 19. November 2025, 14:13 by Franjo
I needed some time to work out the fundamental consequences of this interesting constraint - and gave 3.5* after finishing the solution. But surely this is a wonderful new DFM-episode! Thank you very much for creating and sharing another lovely puzzle.
on 19. November 2025, 10:04 by da-hans
Very nice puzzle. I had to rewind a few times but I agree with the 3 star rating.
on 19. November 2025, 07:44 by damo_89
This is a lovely puzzle
The original puzzle by mathpesto is also lovely (and a little trickier in my opinion)
