ELI5: Explain Like I'm 5

Euler's sum of powers conjecture

Have you ever played with numbers and tried adding them together? Well, a very smart man named Leonhard Euler did that too but with powers (which means multiplying a number by itself a certain number of times). He was wondering if he could add up powers of numbers and find a special pattern.

He tried adding up powers of 2, like 2^1 + 2^2 + 2^3 + 2^4 and noticed something cool: it always ended with the number 6! Then he tried other numbers like 3, and found that it always ended with 9, and with 4 it always ended with 4 or 6.

So Euler made a guess, called a conjecture, that says you can't add up more than 5 powers of any number and end up with a number that ends in 0, 1, 3, 5, 7, or 9. He thought he was right, but he couldn't prove it for sure.

Lots of other smart people studied his guess and tried to prove it, but none of them could. They found some examples that seemed to break the conjecture, so it might not be true after all.

But no one has found a good reason why the conjecture can't be true either, so it's still a mystery. So while we're not sure if Euler's conjecture is true or not, it's still fun to play with powers of numbers and see what we can discover!