ELI5: Explain Like I'm 5

Skewes's number

So, Skewes's number is a really, really big number. So big that we can't even write it down in full. But why is it important?

Well, there's something called the Prime Number Theorem, which tells us how many prime numbers there are up to a certain number. And this theorem relies on something called the Riemann Hypothesis, which we don't really have time to explain, but basically it's a really important math problem that we don't know the answer to yet.

Now, Skewes's number comes in because there's a point where the Prime Number Theorem and the Riemann Hypothesis start to disagree. And we don't know exactly where that point is, but Skewes found an upper bound (which is basically a really big number that we know for sure is bigger than the point where they disagree).

So even though we don't know the exact number where the Prime Number Theorem and Riemann Hypothesis start to disagree, Skewes's number gives us an idea of how big it could potentially be. And that's pretty cool!