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?

(In reply to here are the pairs by Charlie)

Charlie, thanks, good not to have to do the "grey matter" in Excel.

But then in Excel I looked at differences and sums of pairs, even squares and square roots!  I did consider intervals between digits but I see no joy there either.

Rod lists this as D2, s this is something relatively simple!  So....  what have we missed?

Posted by brianjn on 2009-01-11 06:41:25