We’ve chosen a rule that some sequences of three numbers obey — and some do not. Your job is to guess what the rule is.

We’ll start by telling you that the sequence 2, 4, 8 obeys the rule:

Obeys the rule

Now it’s your turn. Enter a number sequence in the boxes below, and we’ll tell you whether it satisfies the rule or not. You can test as many sequences as you want.

When you think you know the rule, describe it in words below and then submit your answer. press this button. Make sure you’re right; you won’t get a second chance.