This is going to be k times k minus 1 times k minus 2, all the way down to 1. In the example where we had 3 heads in 5 flips, this was 3 times 2 all the way down to 1. 3 times 2 times 1. Is there a simpler way that we can write this? This expression right over here is the same thing as k factorial. If you haven't ever heard of what a factorial is, it's exactly this thing right over here. k factorial literally means k times k minus 1 times k minus 2, all the way down to 1.