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Old 2021-09-26, 14:56   #57
charybdis
 
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Apr 2020

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The difficulty of SNFS is determined by the size of the original number, not the composite cofactor, since it's the original number that determines the polynomial. M1217 has 367 digits, so it has SNFS difficulty 367, not 248 (the size of the cofactor). This would be a record size for an SNFS job: I believe the current record is M1193 which had difficulty 360.

(edit: M1217 might be faster by GNFS on the 248-digit cofactor; the record is 250 digits so this is technically within reach if you have thousands of cores, but still far more difficult than M1061, which is comparable to 218 or 219 digit GNFS.)

Last fiddled with by charybdis on 2021-09-26 at 15:02
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