As we have already seen in previous sections, many times we wish to solve equations and
restrict our solutions to the integers. For example, when we find the greatest common divisor of
two integers and then wish to write it as a linear combination, we solve an equation of the form
ax by a b + = gcd( , ). In this case, we have always been able to find integral solutions. These
equations are part of a general class of equations called diophantine equations. Their defining
characteristic is that they only admit integer solutions. These equations are named for the
renowned Greek mathematician Diophantus of Alexandria. Very little is known about the life of
Diophantus, but what is known has been passed down through the years in a mathematical puzzle
that forms, appropriately, a diophantine equation. It goes like this: