Sixteenth note permutations - one beat is one quarter note, and it can hold four sixteenth notes. Mix notes and rests inside that beat and there are 16 different combinations. This exercise works through them all.

Follow along, tap your foot, count out loud, and start palm muting!

Then when you're done, see how you can use this to make music by watching my follow-up here: Random Math Metal Riff Generation Using Pi and the Byzantine Scale

If you're into this sort of thing, you're a prime candidate for my advanced rhythm course, Real Rhythm Guitar: Level 2. This exercise is how it starts, and theres 21 more lessons afterward to expand your rhythmic vocabulary.