For the past year now I've been contributing CPU cycles to a worldwide distributed computing project called GIMPS (Great Internet Mersenne Prime Search) which, as the name implies, looks for massive prime numbers. Well, today they announced they had a found a new world record... a prime number with over 22 million decimal digits! In a more compact form, it is represented as "274,207,281 - 1", a so-called Mersenne prime.
I didn't find the number personally, but I did help by discarding a huge heap of potential candidates, since a single test can take several weeks to complete due to the size of the numbers involved these days. The project has encouraged me to study pure mathematics more deeply and experiment with number theory in general. I have a bit of a love affair with numbers, I'm afraid.
More indirectly, the algorithm is quite an intense stress test for computers, and so far I've blown up a PSU with it! GIMPS also uncovered a hardware bug in Intel's Skylane architecture as well, so it also contributes to more stable computers down the line.
Link to the press announcement - it's also appeared in New Scientist too.