The congruent number problem
was first discussed systematically by Arab scholars of the tenth century.
By the way recall that a positive integer n is a congruent number if it equals
to the area of right triangle with rational sides.
Since tenth century, some well-known mathematicians have devoted considerable energy of the congruent number problem. For example Euler showed
that n = 7 is a congruent number with sides of lenght 24 5 , 35 12 and 337 60 .