Joseph Louis Lagrange

http://en.wikipedia.org/wiki/Joseph_Louis_Lagrange

http://www-history.mcs.st-and.ac.uk/Mathematicians/Lagrange.html

Lagrange's four-square theorem

http://en.wikipedia.org/wiki/Lagrange's_four-square_theorem

http://129.81.170.14/~erowland/courses/2009-2/projects/Nguyen.pdf