This is is my favorite answer on Quora, from Alon Amit.

I came across it when it was making the rounds on the web as a nerd-sniping, faux-meme image designed by some cruel soul. I had no idea what I was looking at. It looked like this:

Diophantine math puzzle

You may have seen such meme images before. They are always pure click-bait garbage: “95% of MIT graduates couldn’t solve this!”, where “this” is some inane, or ill-defined, or trivial brain teaser.

This one is not. The meme is a clever, or wicked, joke. Roughly 99.999995% of the people don’t stand a chance at solving it, and that includes a good number of mathematicians at leading universities who just don’t happen to be number theorists. It is solvable, yes, but it’s really, genuinely hard.

The full response goes into the mathematics needed to arrive at the completely absurd solution. Here’s the link again.