We all love Carol Vodermann (just me then?) and for any maths teachers it has to be a good starter to get students to try the “Numbers Game” just like the channel 4 programme. Now let me be clear this is not an officially endorsed but it works on the same principle and also has the additional benefit that you can manually set the numbers or limit the range (good for lower ability). I have been using this for many years and students never seem to tire from it (within reason). You can download it from here.