The area of a rational right triangle cannot be a square number. This statement is equivalent to "a congruum cannot be a square number."
Fermat's Right Triangle Theorem
See also
Congruum, Rational Triangle, Right Triangle, Square NumberExplore with Wolfram|Alpha
Cite this as:
Weisstein, Eric W. "Fermat's Right Triangle Theorem." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/FermatsRightTriangleTheorem.html