I am permanent resident since sept2006. I will be able to apply for naturalization in sept2009,but now I have to go to work abroad. I accumulated till now like 420 days out of 540 required to apply for naturalization. DO I have to apply for reentry permit or Do I just have to reach the 540 days before sept 2009,without being absent from the USA for more than 6 months consequently? Where can I check exactly how many days I have been physically present in the USA?