Permissions required for the program
The program needs to run INTERNET and ACCESS NETWORK STATE permissions. These permissions are not necessary for the game that does not exchange any information with the outside of your phone or even with the other applications on your phone, but for banner ads provided by Google. Google is committed to a privacy policy for data to be collected through these banners.
Android SDK minimum level
Initially I had in view the lowest level possible to make the game accessible to everyone.
However this minimal level set first to 7 (Android 2.1.x) was changed till 21 (Android 5.0) in order to continue using Google services.