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Katy Perry's latest single is looking at a huge debut sales week. 

"Billboard" says industry sources are now projecting that "Roar" could sell between 525,000 and 550,000 downloads in its opening week out.  Expectations continue to grow, as last week, the single was expected only to hit the 400,000 mark. 

If Katy does make it past 500,000 downloads sold, it will give her easily the largest sales week of 2013 - and possible the largest of her career so far.  Her best single so far was 2010's "Firework," which debuted with 509,000 downloads.