Discovery of a Lost Factoring Machine - Built by a French amateur, E.-O. Carissan, around 1919. Shallit, Williams and Morain include photographs and references to their paper.
The Factor Zone - Aimed at grade school students and teachers, includes course guidelines, worksheets, and factor tables up to 600.
Factoring Papers - Links to papers on the theory and practice of factoring.
Factoris - Online calculator that factorizes large numbers, specified by formula.
Factorization Using the Elliptic Curve Method - Java applet that can be used to find 20- or 30-digit factors of numbers or numerical expressions up to 1000 digits long. It also computes the number and sum of divisors, the Euler's totient and moebius functions, and the decomposition of the number in a sum of up to four squares.
FactorWorld - Dedicated to algorithms and computational results on integer factorization. Includes links to papers, downloadable software, and online resources.
Fermat Search - Leonid Durman's Fermat number factoring site and program.
Known Amicable Pairs - A listing of all the known pairs of numbers, each of which is the sum of the aliquot divisors of the other. Complete for smaller numbers, and extending beyond 200 digits.
N!+-1 Factoring Status - Factoring efforts that have been made so far on numbers of the form n!+-1 using ECM factoring.
RSA Laboratories Factoring Challenge - Numbers representative of those used in the RSA cryptosystem are offered for factor attempts with prizes. A Partition List challenge is also provided in order to encourage work on factoring in general.
Sierpinski Problem - Sierpinski proved there exist infinitely many odd integers k such that k*2^n+1 is composite for every n. Ray Ballinger coordinates a search to prove or disprove whether k=78557 is the smallest solution.
The XYYXF Project - A collaborative project to produce the factorizations of x^y + y^x for 1<y<x<101.
Factoring Fermat Numbers - Cash prizes for new factors of Fermat numbers Fn, for n = 12 through 22. (December 31, 2004)
Factorization of RSA-155 - Announcement of factorization of a 512-bit RSA key using the General Number Field Sieve (GNFS). (August 22, 1999)
