Since the dawn of time [citation needed], mathematicians have been fascinated with what prime numbers are, how many there are (see below), tests for primality, and crucially, finding a pattern in which numbers are prime and which aren’t. So far, the answer to that one has eluded us.

I don’t think it’s too much of an overstatement to say that prime numbers are the building blocks of numbers. They’re the atoms of maths. They are the beginning of all number theory...

Open Season: Prime Numbers (Part 1) By Katie Steckles Aperiodical.com