Doomsday Trainer

This Android app helps you train the Doomsday Algorithm which allows you to quickly deduce the day of the week to any given date within seconds.

It was invented by John Conway in 1973. Here, a variant is used which was found by Fong and Walters in 2010.

For more information and an in-depth explanation please see the Wikipedia article. But the app contains a condensed explanation and detailed practice modes for the three major steps in the algorithm.

It's also out on the Google Play Store.