In the window of my pocket calculator, I can see a six-figure number, abcdef, with distinct digits between 1 and 9. A close inspection of the digits reveals that abcdef, cdef, and def are all prime numbers.

If I turn the calculator upside-down, I see that uvwxyz and wxyz are also prime numbers.

Which number is displayed in the window of my pocket calculator and what is the upside-down version of it?

Full credit for this problem goes to Ajit Athle who has very kindly given his permission for the puzzle to be posted here.

(In reply to Solution without Internet search or Excel by Charlie)

Should I have listed my subject as "Solution without Computer Programming"? ;)

I will grant that both methods are brute force, and logic is not required for solving this problem.

Posted by Leming on 2006-12-15 11:40:57