When a new account is created it is assigned the number which is one greater than the current highest account number. If an account is deleted, its number is not reused, unless it was the highest account number in the file. So if the highest number is 2015, and account 2000 is deleted, the next account will be assigned 2016. But if 2015 is deleted, the next account will be 2015.

 

If an account has been deleted, it is possible to reuse that account number by re-inserting it in a separate procedure. To go this, go to Options > Miscellaneous > Insert missing account number.