There's a more detailed discussion at "A Survey of Equal Sums and Power" by L. J. Lander, T. R. Parkin and J. L. Selfridge http://www.jstor.org/stable/2003249 h

There's a more detailed discussion at "A Survey of Equal Sums and Power" by L. J. Lander, T. R. Parkin and J. L. Selfridge http://www.jstor.org/stable/2003249 http://www.jstor.org/stable/2003249 (under 5.1.n)