The Times Samurai Su Doku 13

Challenge yourself with number puzzlesFor anyone who loves the challenge of Su Doku but manages to solve them within minutes, you can now enjoy the extended mental workout and ultimate endurance test of a five grid interlinked system.

This is Su Doku multiplied: every column, row and 3x3 box must contain the digits 1 to 9. Where the puzzles overlap, the rows and columns do not go beyond their usual 9x9 length but the interlocking boxes give you more clues - and more complexity.

With another 100 new Samurai puzzles to vex you for hours, lose yourself in the four levels of this book:

10 Easy 40 Mild 40 Difficult 10 Super difficult

Even the speediest of Su Doku solvers will be agonising over these ultra-complex, extended brainteasers.

These are the most difficult Su Doku puzzles in The Times range.