Navigator arbitrarily assigns its account numbers and you have no control over that. By the way, Navigator also uses similar number for Categories and Groups in the Chart of Accounts.

If your accounting system needs account numbers, some users just add that number as part of the account name:
    123-456 Utilities/Business

You can then use pre-qualifiers to print reports for just account numbers starting with 123 or 123-4, etc. Search Navigator help for “pre-qualifiers” and see <"http://www.finnav.com/ubb/Forum13/HTML/000020.html">Including account numbers on reports.