A thief breaks into a rich (sure!) mathematician's house while the guy is on vacation. And he finds a safe! (Happy)

But from his experience he knows that he has only one chance to open this kind of safe (I made that up) (Sad)

He looks around in the room for any clues. And lo and behold he finds a card full of numbers hidden in a Math book. (Happy) He is certain that the clue is in that card. But what and how, he asks.(Sad)

What combination should he use to open this safe??enter image description here

  • 1
    $\begingroup$ Riddle? And not locks? $\endgroup$ – n_plum Jun 29 '17 at 22:48
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    $\begingroup$ Lucky for the thief, it seems the safe is unlocked ;) $\endgroup$ – BreakingMyself Jun 29 '17 at 22:59
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    $\begingroup$ FYI, some mathematicians really are rich, usually via working in finance. The best example would be this guy, who was an outstanding mathematician and one of the most successful hedge fund managers ever: en.wikipedia.org/wiki/James_Harris_Simons $\endgroup$ – Gareth McCaughan Jun 29 '17 at 23:30

The combination is:



The roman numerals when converted to A1Z26 is EMIRP, which is PRIME spelled backwards. The combination is a backwards prime. 31081 is a prime number, so the combination is 18013.


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