When Am I Going to Use Prime Numbers?
A timeline shows primes took about 4,000 years to become useful (cryptography); a teacher admits Legendre's conjecture might take a while too.
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Cartoon by Ben Orlin, Math with Bad Drawings. https://cartoons.mathwithbaddrawings.com/2020-05-11-when-am-i-going-to-use-prime-numbers/ (CC BY-NC 4.0)Transcript
[Timeline] 2000 BCE: "study of prime numbers begins" … 2000 CE: "study of prime numbers becomes actually useful"
[Board] "Conjecture: for any n, there exists p prime such that n² < p < (n+1)²." Student: "Ugh. When am I ever going to use this math?" Teacher: "I'll be honest. It might take a while."