For some reason, I looked at this post again. Sorry about the late reply.

The way you would normally handle that scenario is to store the number as a number, then put a mask on it when displaying or printing it. So a 1 can be stored as a 1, but can easily be printed/displayed as 0001. The rule of thumb is you apply formatting at the time you want a user to look at it.

This is assuming there wasn't a reason to have non-numeric characters in the cheque number sequence.