A new type of Sudoku is whetting the appetites of puzzle fans.

**Sandwich sudoku** follows the same rules of sudoku but includes extra clues outside the grid like this:

The clues on the outside of the grid show the sums of the numbers *sandwiched* between the 1 and the 9 in that row or column.

I love it. It’s much more interesting than regular Sudoku. Click here for a printable sheet of three examples.

(Also in today’s column: the best entries to my tangram competition – scroll below.)

I was alerted to sandwich sudoku by crossword champions Mark Goodliffe and Simon Anthony, who run the YouTube puzzle channel Cracking the Cryptic. (Mark has won the Times crossword championship 11 times). They featured sandwich sudoku in March, and were stunned to see the video clock more than 500,000 views – about one hundred times more than than what they normally get for their sudoku clips.

“I think people are realising it has a surprising amount of depth to it. Some of the logic is deep and quite beautiful, plus it appeals to a lot of solvers who enjoy the interaction of maths with basic Sudoku,” says Simon.

Sandwich sudoku is intriguing because the grids often start with very few given numbers in the grid. The example below has only one.

This is a 6×6 grid, but Sudoku still rules apply. Every row, column and 2×3 box must contain the digits from 1 to 6. The clues on the outside of the grid show the sums of the numbers sandwiched between the 1 and the 6 in that row or column.

I’ll start you off. The 12 under the first column means that the numbers between 1 and 6 sum to 12. Using the available digits – 2,3,4 and 5 – there is only one way to make 12, which is 5 + 4 + 3. So we know the squares in orange below must be some permutation of 3,4, and 5. The cell below must be 6, leaving the bottom cell to be 2. Likewise, the green cells must be some permutation of 2,3 and 5, which fixes the positions of 6 and 4.

We continue in this way. There are two ways to make 7, either 2 + 5, or 3 + 4, some permutation of which is in the blue cells. It takes three cells to make 10, marked purple. The cell above the purple cannot be 6, since there is a 6 already in the box, so it must be 1.

Sandwich sudoku has appeared at the World Puzzle Championships for many years, where it is known as ‘Between 1 and 6 Sudoku’, and ‘Between 1 and 9 Sudoku’. Those names are never going to catch on, so I gave it a new name. My column, my rules.

Sandwich sudoku was unknown beyond the hard core competitive puzzle community before Cracking the Cryptic turned it into a YouTube sensation. I urge you to try it out – it’s really fun. What better way to spend the British May bank holiday! Click here for a printable sheet of three examples including the two above.

Here’s the original video if you want more help:

I’ll post the solution grids at 5pm UK later today, as well as hints on how to solve the most fiendish one.

My last column was about the tangram, a well-known puzzle in which seven pieces – five triangles, a square and a rhomboid – are arranged to make a shape. I asked readers to come up with contemporary designs. My two favourite ones are Donald Trump, by Ned Ludd, from Santa Rosa:

And Salt Bae, the Turkish celebrity chef whose method of slicing meat became an internet meme, by Eymen Erdem, from Ankara. He’s got the strut just right!

Please keep on sending me new tangram designs. You can use Mathigon’s interactive tangram solver to create patterns and download them.

*I set a puzzle here every two weeks on a Monday. I’m always on the look-out for great puzzles. If you would like to suggest one, email me.*

*I’m the author of Football School, a book series for 7 to 12 year olds that opens up the curriculum through football. Football School Star Players: 50 Inspiring Stories of True Football Heroes is just out.*

*Together with the Guardian, Football School has launched the Young Sportswriter of the Year competition. Open to all 7 to 12 year olds in the UK, write a 600 word story about sport and you could win a trip to a Premier League game and your story published by the Guardian. For more details click here. Please spread the word among teachers and parents. The last date for entries is May 19.*