Can you prove in general that $\displaystyle 4/n = 1/x + 1/y + 1/z$, where n is a natural number greater than 1 and x,y and z are whole numbers? (this is the Erdos-Straus conjecture of 1948 - to date no one has proven it nor furnished a counterexample).

The last puzzle for CB was too easy. I think this one should keep CB busy for awhile if he wants to try his hand at it.

Good luck to everybody.