University of Regina (Canada)
University of Regina: Math Central: Greatest Common Divisor and Least Common Multiple
Learn about the greatest common divisor, the least common multiple, and the Euclidean Algorithm. This resource gives a description of each of these concepts, accompanied by several examples.
Wolfram Research
Wolfram Math World: Golden Ratio
Math World explains the Golden Ratio, gives the formula for finding the irrational number, and expresses this value as an infinite series. Also defines and represents the Ratio geometrically, its relationship to the Fibonacci numbers,...
Other
Greatest Common Factor Calculator
Free online calculator provides help with finding the greatest common factor.
Wolfram Research
Wolfram Math World: Euclid's Algorithm
This site from Mathworld.com provides a very detailed description of Euclid's algorithm of common divisors and a method of finding the greatest.