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Old 2020-05-17, 10:26   #2
JeppeSN
 
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"Jeppe"
Jan 2016
Denmark

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Found a factor of one of them:
Code:
        p:  factor of 2^{p+1} - 3
----------------------------------
        2:  prime
        3:  prime
        5:  prime
        7:  11
       13:  prime
       17:  11
       19:  prime
       31:  9241
       61:  37
       89:  1823
      107:  11
      127:  11
      521:  193
      607:  11
     1279:  98807
     2203:  47
     2281:  131
     3217:  11
     4253:  23
     4423:  313
     9689:  289935200473
     9941:  419303
    11213:  composite
    19937:  11
    21701:  composite
    23209:  37
    44497:  11
    86243:  6553
   110503:  313
   132049:  composite
   216091:  23
   756839:  757
   859433:  193
  1257787:  11
  1398269:  96997
  2976221:  1451
  3021377:  11
  6972593:  103869349
 13466917:  11
 20996011:  86183
 24036583:  59
 25964951:  76382783
 30402457:  11
 32582657:  11
 37156667:  11
 42643801:  38334482051
 43112609:  59
 57885161:  193
 74207281:  unknown!
 77232917:  11
 82589933:  37463
/JeppeSN
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