Online Puzzle and Sudoku Competitions

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.

Dutch Championship 2026

Preparations for the 2026 Dutch Championship are underway again! The qualifiers will take place online, from Friday March 6th 2026 at 12:00 (CET) until Monday March 9th 2026 at 11:59 (CET). The live championships will take place on Saturday 2026.. Keep an eye on this website for more information!