1. Appbrain,
http://www.appbrain.com/stats/number-of-android-apps
2. Tiuri van Agten,
http://www.distimo.com/blog/2012_01_google-android-market-tops-400000-applications
3. Beth Stackpole,
http://www.computerworld.com/s/article/9217885/Your_next_job_Mobile_app_developer
4. Dan Rowinski,
http://readwrite.com/2012/02/06/infographic_history_of_mobile_app_stores
5. Steve Lohr, from
http://www.nytimes.com/2010/07/12/technology/12google.html?_r=0
(2010)