Factorization Using the Elliptic Curve Method
- http://www.alpertron.com.ar/ECM.HTM
- 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.
Known Amicable Pairs
- http://amicable.homepage.dk/knwnc2.htm
- 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.
Sierpinski Problem
- http://www.prothsearch.net/sierp.html
- 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.