Sometimes known as hidoku or hidato, you are given a sparse grid with just a few key squares pre-filled. You must then fill in an ascending sequence of numbers going sideways or diagonal.

Play 36 levels of different size grids for free with no adverts!

If you enjoy the free trial, buy the full game or some keys to unlock more than 600 levels ranging from easy 3x3 grids, or tough 12x12s - best played on tablets.

No timers, music or annoying sound effects - take your time and take on the challenge of the Number Knot!

Tip: There's no need to start from 1 and work all the way to the end, you can jump around and fill in any easy sections first and join them together at the end.