Randomly scramble the digits 0, 1, 2, 3, 4, 5 and 6 to form a seven-digit number (or a six-digit number if the leading digit is 0). Rank the following events in order ...

The number 1 has one digit and is divisible by 1; 12 has two digits and is divisible by 2; 123 has three digits and is divisible by 3. Which new digit (not already used) can be added to the end of 123 ...