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Combination Lock Phil buys a four-figure combination lock where each dial can be set from 0 to 9, and needs to decide what number to set to unlock it. He opts for a number with all different digits and a leading zero so he only has to remember a three-figure number. When the chosen number is set for the lock to open, nine other four-figure numbers are visible. For instance, if he chooses 0123, then 1234, 2345, 3456, 4567, 5678, 6789, 7890, 8901 and 9012 are all visible. As a retired Maths teacher with a natural interest in numbers he examines the other nine numbers that are displayed when the lock is set to open. None of these numbers are prime but two of them