Factoring numbers is a concept learnt with the introduction of divisibility in schools, yet the process can be exceptionally challenging and difficult. This category addresses topics from the basic divisibility tests to perfection and the general problem of extracting prime factors.

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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.
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.
Factorizations of Near-repdigit Numbers
Factorizations of numbers composed of all the same digit except first and/or last.
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.
Integer Factorization
Paul Leyland's list of his own and other factorisations.
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)
[Mozilla Einstein]
Last update:
March 15, 2015 at 19:19:27 UTC
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