Knuth talks about this in the later editions. I seem to recall that this is Volume II. It's in one of the exercises. At 08:02 AM 12/4/02 -0800, Eugene Salamin wrote:

--- Don Reble <djr@nk.ca> wrote:

...

I think the two-square-sum problem has been done to death. If you can factor X, it's easy to determine whether it has such representations; does anyone know how to generate them?

Maple has a function "sum2sqr" which lists all the representations. You could examine the code.

Gene