from Wikipedia: 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. Prime numbers give rise to various generalizations in other mathematical domains, mainly algebra, such as prime elements and prime ideals. read more below: http://en.wikipedia.org/wiki/Prime_number http://arstechnica.com/science/2013/02/ask-ars-why-spend-time-and-money-finding-new-prime-numbers/
Interesting Borek. I had to investigate: http://www.businessinsider.com/why-are-cicada-lifespans-prime-numbers-2013-5
Poor Hardy! He went to his grave proud of the uselessness of number theory. Strange that a discipline studied for millennia suddenly became useful only a couple of decades ago.