If A^x + B^y = C^z, where A, B, C, x, y and z are positive integers and x, y and z are all greater than 2, then A, B and C must have a common prime factor.

Source : bealconjecture.com

The conjecture was proposed in 1993 by self-taught mathematician Andrew Beal, who was working on aspects of Fermat's Last Theorem.

The American Mathematical Society is holding in trust a $1,000,000 prize fund for anyone who can prove (or disprove) the conjecture.