What is Euclid's theorem?

Euclid's theorem states that there are infinitely many prime numbers. This was first proven by the ancient Greek mathematician Euclid in his work "Elements." The proof involves assuming a finite number of primes, constructing a new number by multiplying them together and adding one, which cannot be divisible by any of the assumed primes, thus leading to a contradiction. Consequently, this implies that primes cannot be finite, confirming their infinitude.