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Let f(n) be the sum of the positive integer divisors of n. If n is prime and f(f(n)) is also prime, then call n a bouncy prime. What is the smallest bouncy prime?

 Jun 7, 2020
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can you help me with loci

 Jun 7, 2020
 #2
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Let f(n) be the sum of the positive integer divisors of n. If n is prime and f(f(n)) is also prime, then call n a bouncy prime. What is the smallest bouncy prime?

 

3 is prime.  It has positive integer divisors 1 and 3, so f(3) = 4.  

4 has divisors 1, 2 and 4, so f(4) = 7 which is prime.

Hence n = 3 is a bouncy prime.

 

This doesn't hold for n = 2, so n = 3 is the smallest bouncy prime.

 Jun 8, 2020

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