With impeccable timing, just in the middle of my series about primality testing, a new Mersenne prime has been announced, a little under two years after the previous one. In particular, it has been shown that is prime; this is now the largest known prime number.

If you want to understand what computers are actually doing when they check a Mersenne number for primality, I wrote a whole series about it two years ago: visit this list of my post series and search for “Lucas-Lehmer”.