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 re: Solution without Internet search or Excel by Leming)

With using the same logic that Leming had used, but instead of the primes page, I had use the internet site Factoris (http://wims.unice.fr/wims/wims.cgi) to verify the primes.  Nonetheless, I had come to the same pocket calculator entry as did Leming (and Charlie)...

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Edited on December 15, 2006, 2:05 pm

Posted by Dej Mar on 2006-12-15 14:03:35