perplexus.info :: Probability : (x!+1)/(x+1) = prime number

(x!+1)/(x+1) = prime number (Posted on 2010-07-30)

For a positive integer x drawn at random between 1 and 20000 inclusively, determine the probability that (x!+1)/(x+1) is a prime number.

No Solution Yet Submitted by K Sengupta

Rating: 2.3333 (3 votes)

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re(2): computer can't go that high

| Comment 3 of 9 |

(In reply to re: computer can't go that high by Justin)

I see the prime divisor function (PRMDIV) in UBASIC doesn't even try with numbers as large as the 10513391193507374500051862069 that's encountered when x=28, which is why my program missed it.

Posted by Charlie on 2010-07-30 18:17:40

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