A pair of emirps consists of two prime numbers such that reversing the digits of one number gives the other. How many pairs of two-digit emirps exist such that each number in the pair is greater than 11?

1 answer

1. The list of prime numbers between 11 and 100 are:
   
   11 13 17 19 23 29 31 37 41 43 47 53 59 61 67 71 73 79 83 89 97
   
   So try them one at a time, say
   number reversed
   11 11 OK
   13 31 OK
   17 71 OK
   19 91 is composite [pair rejected]
   23 32 [rejected]
   ...
   97 79 OK
   
   So you'll get a list in no time.

   Answer ID
   524607

   Created
   April 3, 2011 12:41pm UTC

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   0

   URL
   https://questions.llc/answers/524607