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Divisibility

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Division Rules (8)		Software *(59)
Perfect Numbers (13)		Tables (12)

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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.

FactorWorld - Dedicated to algorithms and computational results on integer factorization. Includes links to papers, downloadable software, and online resources.

Factoring Theory - A thorough summary of many major factoring algorithms. Includes some source code on many pages, and gentle introductions to the more complex methods.

Factoris - Online calculator that factorizes large numbers, specified by formula.

Factorization Applet - An online Java applet that takes a number as input and outputs its prime factors.

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.

Factorization of F10 - F10 = 2^(2^10) + 1 is the 10-th Fermat number. Richard Brent details his discovery of the two largest factors.

Fermat Search - Leonid Durman's Fermat number factoring site and program.

I Love Binary, Primes, and Factors - Divisibility, primes and binary numbers.

Integer Factorization - Paul Leyland's list of his own and other factorisations.

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.

Proth Factors - The current search status for factoring Proth numbers (k.2^n+1).

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.

Record Factors Found By Pollard's p-1 Method - Some numbers have factors that are easily discovered by the Pollard method. Andy Steward explains the method and lists record factors obtained by it.

Robinson Primes - An analysis of problems relating to the numbers k.2^n+-1, primes, and factor patterns, including the Sierpinski problem.

Sam Wagstaff - Article about SNFS factorisation of 3^349-1.

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 Factor Zone - Aimed at grade school students and teachers, includes course guidelines, worksheets, and factor tables up to 600.

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