Can you fill a 4x4 square so each row and each column forms a prime number? And a 5x5 square?
Note: in both cases, there should be no duplicate rows or duplicate columns. Also, numbers cannot start with a 0. Finally, all digits from 0 to 9 should be used at least once.
With first row and column chosen at random (except for avoiding digits zero) from a list of primes:
4651
2309
9587
7919
Since those numbers were chosen at random, and then the rest chosen to fit, there are probably more.

Posted by Charlie
on 20050719 15:48:51 