On page 384 of the book "Number Theory:Volume 1:tools and Diophantine Equations" by Henri Cohen there is reference to the fact that: "It has been proved by Schinzel, Mordell nd successors that such an identity does not exist..."
Can someone give me a reference hopefully to a paper available on the Internet. I don't have access to Cohen's book, only to an excerpt from the book available on the Internet.