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Old 2017-01-26, 01:02   #1
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Nov 2016

22·79 Posts
Post Primes of the form n+-phi(n)

Is there a way for finding all the primes < 1000 (or greater bound) which have the form n+-phi(n) (Just a reminder that phi is Euler's Phi Function.) The first such primes of these forms are 15-phi(15) = 7 and 15+phi(15) = 23. A list of numbers n such that n-phi(n) and or n+phi(n) are prime would also help here. Thanks.
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