" 

 == top selling by years == 

  2013  Robin Thicke's ""Blurred Lines,"" featuring Pharrell and T.I., was 2013's top selling song, with 6.5 million sold. 

  
 http://www.billboard.com/articles/news/5855151/justin-timberlakes-2020-2013s-best-selling-album-blurred-lines-top-song 

 and 
 I would note this to add to the achievements   
 Katy perry's Roar is her 7th single to superpass the 4 million market and it's her 6 song to do so 

   "