On Feb 25th 2003, NFSNET completed the factorization of 11^197+1.

The factors of the C161 cofactor are:

p76 = 9892817292333841349326992570525012475558072147134506608232615478288870172703 and

p85 = 18400145893299637845956243751134784535212088367350484039252741250979697362505 \
         06946877

We used SNFS with the polynomials x-m and x^6+11 which share a root m=11^33 mod 11,197+. As in previous factorizations, we used primes up to 40 million on the rational side and 50 million on the algebraic, with up to two large primes < 500 million on each side.

The sievers started work on 2nd January and finished on 30th January. At least 28 people contributed (some work was recorded as being done by "unknown" and it's no longer possible to know to how many other people that corresponds) using at least 80 computers. They found 44,739,616 relations which were reduced to a matrix which had 4,880,514 rows and 4,894,823 columns. The linear algebra took 120 hours elapsed, circa 1800 hour total cpu time on 30 PIII-1000 processors of the MSRC cluster. The factors were found on the first dependency.

Our thanks go to all the contributors for their efforts and to CWI for letting us use a modified version of their NFS software.

NFSNET Administration:
Jeff Gilchrist, Don Leclair, Paul Leyland, Richard Wackerbarth

Contributors (alphabetical order): Brian Beesley, Chris Card, Francois Grieu, Alex Kruppa, Rick Lavoie, Igor Schein, Martin Schroeder, and 17 others who have not selected to be listed here.