Posted by Sara on Saturday, April 2, 2011 at 8:09pm.
A pair of emirps consists of two prime numbers such that reversing the digits of one number gives the other. How many pairs of twodigit emirps exist such that each number in the pair is greater than 11?

algebra  MathMate, Sunday, April 3, 2011 at 8:41am
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.