Oh I see it could by divided by another number as well. I’m not seeing the amazing significance.
Primes lie at the core of Number Theory. There are tons of amazing facts about them. Many important theorems have been proven about them. Many others defy proof (and hold back number theory because of it), etc. Take any elementary algebra course and you will begin to learn about primes. Ten years later as you are finishing up your PhD in mathematics, it’s likely you will STILL be learning things about them.
Oh, and then the practical things are there as well. Just Google ‘encryption and prime numbers.’ Prime numbers are extremely important in safeguarding our nation’s secrets. Figure out a way to break today’s codes (you will necessarily be working with prime numbers), and you will probably very quickly find yourself kept under lock and key! Well, I don’t know about the latter, but you will probably be sworn to secrecy and be forbidden to publish anything on the subject in the open marketplace.
Man, you needed a fun math teacher in 4th grade like Mr. Mellon.
We had fun with this one day I obviously haven’t forgotten in over 4 decades.
https://en.wikipedia.org/wiki/Sieve_of_Eratosthenes