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