Taxpayer ID of a Supplier

Yesterday i was trying to create few suppliers in my test system. In supplier page, "Taxpayer ID" is a mandatory column. So i used a sequence of 9 digit number. That random number matched with some supplier that i must have created earlier. I tried few times and all the the time, "Taxpayer ID" was duplicate value. I thought to write a query that can give me a 9 digit number that is not used as "Taxpayer ID" of a supplier. But i did not know how to write that query.

Today i saw this post http://jonathanlewis.wordpress.com/2012/09/18/minimum-stats/. it has following query to generate list of sequence numbers.

select --+ materialize rownum id from dual connect by level <= 1e4

This query gave me idea to generate unused taxpayer Id

SELECT id FROM (SELECT rownum + 100000000 id FROM dual CONNECT BY level < 1e9 ) tax_ids WHERE NOT EXISTS ( SELECT NULL FROM ap_suppliers WHERE num_1099 = tax_ids.id ) ;