HSSC has started!

The Holiday Season contest has started!
Click here to go to the participation page.

Enjoy the test and happy Holidays!

Practise sudoku #8 - Consecutive Sums

This is already the last practise sudoku. A pretty new variant that has a lot of potential in contests and competitions: Consecutive Sums. We received a lot of positive feedback on this type in the IB.
Tomorrow (24 December at noon CET) the contest will start. We hope and expect that the practise sudokus have helped to come ‘in the mood’ and help to understand the ins and outs of the new(ish) types. Good luck with the contest and don’t forget: Enjoy!

Merry Christmas to all of you.

Practise sudoku #7 - Anti Knight

We hesitated about how useful it is to have also an Anti Knight sudoku to practise, since those sudokus can be found at all places on the internet. But we had a few spare ones after writing, so we might as well publish it here too. This Anti Knight has the given digits only in the top right and bottom left corners, so there is a beautiful serene wide open space to be filled with digits. Enjoy! 🙂

Difficulty levels of the practise sudokus

We received some feedback on the difficulty levels of the practise sudokus; players found some of them to be very tough nuts to crack.
We can reassure you that indeed some of them are actually harder than the contest puzzles, so don’t be scared off by the difficulty of the practise sudokus! In our opinion it is better to practise with a harder puzzle than with an easier one. The easier ones are in the Instruction Booklet.

Practise sudoku #6 - Sum or Product Frame

After the writing of all the sudokus and the selections, HSSC turned out to be a bit more math-oriented as expected. This Sum or Product Frame requires quite a bit of calculating too. It is really helpful to have a small table of possibilities for all the sums and products available before the contest starts. This practise puzzle contains a lot different clues. Use it to your advantage! 🙂

Practise sudoku #5 - Weiqi

Weiqi was introduced during WSC2024 in Beijing and has a lot of interesting calculations to offer. Use the fact that all dots are placed!

Practise sudoku #4 - Position Sums

Position Sums has become a favorite type for Richard to write. The possibilities for entries in this type seem endless.

Practise sudoku #3 - XV

The negative constraint plays an important role in this XV sudoku!

Practise sudoku #2 - Diagonal

The many given digits in rows 3-7 provide an easy start, but solving gets gradually harder in this Diagonal Sudoku.

Practise sudoku #1 - Mathrax

This Mathrax sudoku was too hard to use in the contest, but since it has everything in it for a good Mathrax sudoku, it is very well suitable as practise material. 🙂 Enjoy!
Sudoku – Mathrax

This practise sudoku was featured on the CtC video channel. You can find the solve video here.

HSSC - Holiday Season Sudoku Contest

After our succesful 10 year anniversary contest, we now present a sequel: The Holiday Season Sudoku Contest; 8 tough sudoku variants to solve in 2,5 hours.
You can read more about it here on the website via the menu on the right, as well as in the instruction booklet (IB) here.

Extra puzzles with solve hints
Three of the types that are in the contest were also part of the special Sudoku Advent Series, complete with solve hints on the second page of each pdf.
Since not all players might be aware of this Advent calendar, we think it is appropriate to publish these puzzles here too, so everybody has the same information. In the remainder of the Advent calendar, there are no more types that are also in HSSC.

Here are the Advent puzzles:
Day 1 -Position Sums
Day 4 – Sum or Product Frame
Day 14 – Consecutive Sums (updated version; removed one possibility (15) for sums that can be formed only in two ways in the solve hints. Apologies!

More practise puzzles
We enjoyed writing this contest so much that we have a lot of spare puzzles. So for each variant in the contest there will be an extra practise puzzle. They will be published one per day, starting on Tuesday the 16th.

NK 2026

De voorbereidingen voor het NK 2026 zijn weer begonnen! De kwalificaties vinden online plaats, van vrijdag 6 maart 2026 12:00 (CET) t/m maandag 9 maart 2026 11:59 uur (CET). De live kampioenschappen vinden plaats op zaterdag 2026. Hou deze website in de gaten voor meer informatie!