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(Meta comment: Congrats to Andre Nicolas! I am happy for Andre Nicolas that he is second ranked now. Also he has 3001 answers with no questions. That is good. I am also glad to see Arturo Magidin has been online yesterday.)

Now my question is the following: What prime numbers have the sum of their digits as a prime number? We know that $3001$ (could be Andre's $3001$ answers) is a prime number with the sum of its digits a composite number. How many primes are there such that their sum of their digits is prime?

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    In base 2, every Mersenne prime qualifies. And every Fermat prime, for that matter.2012-10-19
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    Reminds me of [http://en.wikipedia.org/wiki/Rider_(legislation)](http://en.wikipedia.org/wiki/Rider_(legislation))2012-10-19
  • 0
    Generalising Tanner L. Sweet's first comment: [Repunit primes](http://en.wikipedia.org/wiki/Repunit#Repunit_primes) qualify in any base.2012-10-19

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