If games that challenge your speed and perception intrigue you, then you might want to check out the free Android puzzler 123 Memory: The Numbers Game.
One level at a time, 123 Memory introduces a series of numbered buttons, teaching you the basics with just two at first, before moving on to three, four, five, and so on.
In each level - timed simply by a translucent layer crossing over the screen - the numbers remain only for a split second.
After they disappear, it's up to your own memory to determine which order to press them in.
The mechanics are simple, and the interface even simpler, making for a pretty smooth experience.
You can change the game to portrait or landscape mode in the options menu, and enable "night mode" to make the color scheme easier on the eyes.
Grab 123 Memory: The Numbers Game for free on Google Play.