Factoring Cunningham Numbers

Most Wanted Cunningham Number (2^647)+1

Dear Lattice Siever,

This is a project that factors a 169-digit number, using the Special Number Field Sieve (SNFS). This specific Cunningham number, p647, appears on the list of wanted numbers issued September 18, 2001 with the publication of the 3rd edition of the Cunningham Tables (cf. The Cunningham Project ). The program collects data used to build a large matrix, precisely the same method used to break RSA-keys. Depending upon the results of preliminary work presently in progress, we may continue with the next RSA Challenge number, RSA-576, when sieving for p647 finishes (cf. The New RSA Factoring Challenge ).

The program claims to want 64Mb of RAM, but runs well with smaller amounts. If you have under 96Mb of RAM, you might try using 40Mb, which runs well on Lehigh's public sgi sites. NOTE: All programs and initialization files are copyright Arjen K. Lenstra, as indicated.

This smallish number most likely will not be distributed, but the input file is available here r647 . The test range rv64 , gives the output file mem64, when used with the same binary as for the previous Cunningham factorization cu5283p .

An account of the earlier factorizations of 5^283+1 and the Mersenne number M727 posted by Peter Montgomery (to the nmbr_theory list and the Mersenne list) is available here .