Use APKPure App
Get Sage old version APK for Android
The Sage Android App
Android client for the Sage open-source mathematical software system.
Please use http://groups.google.com/group/sage-devel for feedback until the release is finished!
GPL source code at https://github.com/sagemath/android
For a good keyboard app to use in conjunction with Sage Math, have a look at Hacker's Keyboard in the playstore.