Published online by Cambridge University Press: 26 September 2016
Let $a,b,c$ be a primitive Pythagorean triple and set
$a=m^{2}-n^{2},b=2mn,c=m^{2}+n^{2}$ , where
$m$ and
$n$ are positive integers with
$m>n$ ,
$\text{gcd}(m,n)=1$ and
$m\not \equiv n~(\text{mod}~2)$ . In 1956, Jeśmanowicz conjectured that the only positive integer solution to the Diophantine equation
$(m^{2}-n^{2})^{x}+(2mn)^{y}=(m^{2}+n^{2})^{z}$ is
$(x,y,z)=(2,2,2)$ . We use biquadratic character theory to investigate the case with
$(m,n)\equiv (2,3)~(\text{mod}~4)$ . We show that Jeśmanowicz’ conjecture is true in this case if
$m+n\not \equiv 1~(\text{mod}~16)$ or
$y>1$ . Finally, using these results together with Laurent’s refinement of Baker’s theorem, we show that Jeśmanowicz’ conjecture is true if
$(m,n)\equiv (2,3)~(\text{mod}~4)$ and
$n<100$ .