Unlock Android

In 2008 Google introduced a new way to unlock their Android phone: the Pattern Lock Screen. You have to connect a number of at least four dots in a three by three grid to unlock your phone. There are many combinations possible. In the great Online Encyclopedia of Integer Sequences (oeis.org) I found the number of possibilities in entry A163889.

In this plot you see all 1624 possible patterns for the shortest length of four dots. I found a list of all patterns here: https://github.com/delight-im/AndroidPatternLock.