digits | factor | from | B1 | sigma | date | who |

55 | 7523020307427066273763456609903850552762967576510974081 | 10^{260}+1 | 43e6 | 3933468262 | 24 Jun 2004 | B. Dodson |

55 | 1268413494411135671239686038243358243539607519968737801 | 3^{1557}+1 | 43e6 | 1073421943 | 18 Nov 2004 | K. Aoki |

54 | 477350833522476258826705274670317082147893737193497151 | 3^{577}-1 | 43e6 | 1939606094 | 10 May 2004 | K. Aoki |

53 | 54093886887062230599082516017052647105427126977713417 | 3^{508}+1 | 43e6 | 1988971643 | 06 Jun 2004 | B. Dodson |

53 | 42156379589779912226383108151000450094080783333678881 | 2^{845}+1 | 43e6 | 2242386807 | 20 May 2004 | B. Dodson |

53 | 33961207341909494975722524207839732407744380168756907 | 3*2^{653}-1 | 860500 | 879193285 | 07 Oct 2004 | R. Backstrom |

53 | 18489093999230985031269595355473053970276854216314509 | 7^{286}+1 | 43e6 | 1937590108 | 27 Jul 2004 | B. Dodson |

53 | 11984437123431823969432655822865428382472038412325377 | 11^{473}+1 | 43e6 | 3782281521 | 15 Jul 2004 | K. Aoki |

51 | 738313998235889565301599572531640626810525425999201 | 2^{984}+1 | 11e6 | 1073040516 | 26 May 2004 | R. Keiser |

51 | 197093734279293731287445626494587381600438850930731 | 5^{665}-1 | 43e6 | 2891223763 | 08 Nov 2004 | B. Dodson |

**
Lehigh's Beowulf.** Dodson's factors above, five of the top ten
for the year, were found using a beowulf cluster at Lehigh. During
November 1, 2003 to December 31, 2004 there were 122 Cunningham factors
found by ECMNET, of which 42 were found by Dodson using the cluster.
Dodson intends a more narrowly focused effort on factors of 50 digits
or more in 2005.
An analysis of the ECM efforts for the year 1998, when the first factor
of more than 49 digits was found, is given in
Champs. The count of 40 - 49 digit factors was Dodson 22;
Zimmermann 18; Montgomery 12, but the only factor that counted was
Curry's 53 digit factor. (These earlier factors of Dodson were found using
binaries of Montgomery's ECM/FFT program, below.) See also
the all-times all-ecm-programs top-50 table,
and the gmp-ecm top ten from 1998,
1999,
2000,
2001,
2002,
2003.

**History.** Richard Brent has predicted in 1985 in a paper entitled
*Some Integer Factorization Algorithms using Elliptic Curves*
that factors up to
50 digits could by found by the Elliptic Curve
Method (ECM). Indeed, Peter Montgomery found in November 1995 a factor of
47 digits of 5^256+1, and Richard Brent set in October 1997 a new genuine
record with a factor of 48 digits of 24^121+1.

**Goal.** The original
purpose of the ECMNET project was to make Richard's prediction
true, i.e. to find a factor of 50 digits or more by ECM.
This goal was attained on September 14, 1998, when Conrad Curry found a
53-digit factor of 2^677-1 c150
using George Woltman's mprime program.
The new goal of ECMNET is now to find other large factors by ecm,
mainly by contributing to the
Cunningham project, most likely the
*longest, ongoing computational project in history*
according to Bob Silverman.
A new record was set by Nik Lygeros and Michel Mizony, who found
in December 1999 a prime factor of 54 digits using GMP-ECM.

**Free implementations of ECM.**

**Bibliography.** To know how ECM works and the history of the
factorization of Fermat numbers by ECM and other methods, look at the
paper Factorization of the tenth Fermat number by Richard Brent.
Looking at the old paper Some Integer Factorization Algorithms using Elliptic Curves you'll see that very few improvements were made to ECM
since 1985. One of these improvements is the FFT continutation
invented by Peter Montgomery, and detailed in his dissertation entitled
An FFT
extension of ECM.
You might also look at the paper *A Practical Analysis of the Elliptic Curve Factoring Algorithm*, by Bob Silverman and Sam Wagstaff, Mathematics of
Computation vol. 61, July 1993.
People reading german may look at Franz-Dieter Berger's Diplomarbeit
entitled ``ECM Faktorisieren mit elliptischen Kurven''.
Finally, have a look at the
FactorWorld page from Scott Contini.