Instructions

1. Select 'Easy', 'Medium' or 'Tricky' to make a new rule.
2. Enter an input number and leave the output number blank, then press 'Calculate' to see what output number the rule gives. Press 'Record' to keep the result to refer to later. Keep doing this until you think you know what the rule is.
3. Enter a new input number and the output number you think the rule will generate, then press 'Check'. You must do this twice in a row to win.

Note that a rule can be written in different ways. You might have written the rule differently than the computer, but still be right.