Solution of Ljunggren Equation/Mistake

Source Work

1997: David Wells: Curious and Interesting Numbers (2nd ed.):

The Dictionary

$220$

Mistake

The only solution of the equation $x^2 + 1 = 2 y^2$ is $x = 239, y = 13$.

There also exists the solution $x = 1, y = 1$.

It perhaps also needs to be pointed out that the equation is Diophantine.

Sources

• 1997: David Wells: Curious and Interesting Numbers (2nd ed.) ... (previous) ... (next): $239$