Euclidean Algorithm 
Greatest common divisor of two positive integers
An example:
The divisors of \(12\) are \(1,2,3,4,6,12\).
The divisors of \(18\) are \(1,2,3,6,9,18\).
The common divisors of \(12\) and \(18\) are \(1,2,3,6\); among the common divisors of \(12\) and \(18\), \(6\) is the biggest. It is called the greatest common divisor of \(12\) and \(18\).
Another example:
The divisors of \(10\) are \(1,2,5,10\).
The divisors of \(20\) are \(1,2,4,5,10,20\).
The common divisors of \(10\) and \(20\) are \(1,2,5,10\); among the common divisors of \(10\) and \(20\), \(10\) is the biggest. It is the greatest common divisor of \(10\) and \(20\).
