Why are prime numbers important in real life? What practical use are prime numbers?
Ask periodical cidacas why they use prime numbers for the cycle length.
The fact that the surviving periodical cicadas have life cycles built on prime numbers may have conferred key survival advantages. A prime-numbered lifespan means that predators cannot match their own shorter life cycles to the availability of cicada prey. For instance, if the cicadas had even-numbered lifespans, a predator with a two-year life cycle could expect a cicada feast, and a subsequent population bump, every few generations, because all even numbers are divisible by two. As explained in 2001 by a trio of researchers from the University of Chile and the Max Planck Institute of Molecular Physiology in Germany, “a prey with a 12-year cycle will meet — every time it appears — properly synchronized predators appearing every 1, 2, 3, 4, 6 or 12 years, whereas a mutant with a 13-year period has the advantage of being subject to fewer predators.”
Primes are used in several routines in information technology, such as public-key cryptography, which makes use of properties such as the difficulty of factoring large numbers into their prime factors.