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Not a Prime (Posted on 2012-12-20) Difficulty: 3 of 5
Prove that 5100+575+550+525+1 is not a prime number.

No Solution Yet Submitted by Danish Ahmed Khan    
Rating: 3.0000 (2 votes)

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re: answer | Comment 3 of 6 |
(In reply to answer by Dej Mar)

I'd be interested in seeing how these factors were found. My factoring program found 3597751 and 28707251, but got only as far as 56531057 in trial divisors of the remaining 76379660648003781777292087596491819833721077266601195001, which is nowhere near the needed 4032808198751 for the next prime divisor.

But, BTW, the final "prime" factor listed, 4687045214139234043375683501, also fails the prime test, the P value being 60895742403057891673741119:

list
   10   N=4687045214139234043375683501
   20   for Dvsr=12345 to 99999
   30     if N @ Dvsr = 0 then print Dvsr:cancel for:goto *Found
   40     P=modpow(Dvsr,N-1,N)
   50     if P<>1 then print "not prime":print Dvsr:print P:cancel for:goto *Npr
ime
   60   next
   65   print "couldn't prove"
   70   *Found
   80   *Nprime
   90   end
OK
run
not prime
 12345
 60895742403057891673741119
OK

Edited on December 21, 2012, 12:11 am
  Posted by Charlie on 2012-12-21 00:05:37

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