EN
Let a,b and c be relatively prime positive integers such that a²+b² = c². We prove that if $b ≡ 0 (mod 2^{r})$ and $b ≡ ±2^{r} (mod a)$ for some non-negative integer r, then the Diophantine equation $a^{x} + b^{y} = c^z$ has only the positive solution (x,y,z) = (2,2,2). We also show that the same holds if c ≡ -1 (mod a).