Making an autonumber field start at a set number

I am constructing an order number and a Job number based database and I want
the order numbers to automatically increment to the next number, I currently
have used a combined key to achieve this but don't know how to make both
parts of the key display on the form and don't know how to make the number
increment starting from a given number say 550000, can anyone help, possibly
I should not use the key field to achieve the desired effect?



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