Wolfram Research
Wolfram Math World: Clairaut's Difference Equation
This page from Mathworld.com gives a very brief statement of Alexis Claude Clairaut's Difference Equation, also called Clairaut's Differential Equation. (This equation is a special case of Lagrange's Equation.) Includes special links.
University of St. Andrews (UK)
University of St. Andrews: Alexis Claude Clairaut
Contains a lengthy and detailed biography of Alexis Claude Clairaut including information on his relationships to other mathematicians of his day.