ELI5: Explain Like I'm 5

Idoneal number

An idoneal number is a fancy kind of number that is really cool because it has some special properties. Just like how some people have special skills like singing or drawing, idoneal numbers have special skills in math!

You know how when you add numbers together, you get a bigger number? Well, idoneal numbers do something special when you add them up with other numbers. They can only be made by adding two special kinds of numbers together called "primes".

Imagine you have a big cake, and you want to cut it into smaller pieces. You might cut it into halves or quarters, right? Well, idoneal numbers can only be cut into smaller pieces in a special way, like when you cut a pie into equal slices.

These numbers are really rare and special, like a shiny diamond or a rare Pokémon. Sometimes, people spend years trying to find the next idoneal number! And when they do, it's a big deal for math and science.