There are 43 3-digit prime numbers which, when reversed, also yield a prime number. (Eight of these are actually consecutive primes).

Of the 43, 15 are simply palindromes (e.g. 929), but of the remaining 14 pairs of numbers (called 'emirp's), one pair in particular exhibits two unique characteristics, one of which is rather surprising.

What are the numbers, and what are their unique characteristics?

Well, addition of a sort is involved, but not just by adding each pair of primes.  And the 'interesting pattern' arising from subtraction is that the remainders for all pairs indeed equal 198 or a multiple thereof, of which Brian found the two 396's!  But again, nothing particularly unique there.  Try another operation perhaps (and forget the calulator display approach)!   

Edited on January 15, 2009, 1:47 pm

Posted by rod hines on 2009-01-13 11:59:55