About a century later, Euler became interested in the following immediate consequence of this result: An odd integer N that can be expressed as a sum of two squares in two different ways is composite. (That N has the form 4n + 1 clear from reducing the sum of two squares mod 4). The factoring problem associated with this compositeness is, of course, how to find factors of N using the two representations. Here “factoring” means splitting a composite integer N into a product of two factors.