Makes sense 13 and 17 prime numbers make 221 to repeat. 2024 less 221 is 1803
One hypothesis for the reason behind the periodical cicadas’ seemingly inscrutable selections of 13- and 17-year increments for their reproductive cycle centers around the fact that both numbers are prime. The idea is that by popping out of the ground only in prime numbered intervals, periodical cicadas avoid ever synching up with booming populations of predators, which tend to rise and fall on two to ten year cycles, wrote Patrick Di Justo for the New Yorker in 2013.
Mathematically speaking, the logic checks out, but the thousands of cicada species around the world that don’t have synchronized brood emergences in prime increments cause cicada researchers to wonder if this is the whole story. If the periodical cicada’s unique life cycle is so uniquely advantageous, why haven’t the rest evolved similar reproductive strategies?
https://www.smithsonianmag.com/science-nature/14-fun-facts-about-cicadas-180977361/