I was doing some of the previous math contests and faced a question that asked me "the number of two digit primes that are still primes when the digits are reversed".
I actually wrote down every two digit primes and then checked with the condition. Honestly it was not a hard work but it took me about five minutes only for this problem while only 30 minutes are allowed for the whole test of 15 problems. And even more, I made a small mistake of thinking "91" is a prime so got this problem wrong.
So my question is, is there any special shortcut way that I can get the prime numbers quickly and without missing? What should I do if the problem asks me about three or more digit prime numbers?
Thanks! It is #7 of Part 1 [From this test] http://www.wsmc.net/contests/2008_Contest/regtopprob.pdf