The problem of studying positive integers n which occur as areas of rational
right triangle was of interest to the Greeks. 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. It is known that Leonardo Pisano (Fibonacci) was challenged around 1220 by Johannes of Palermo to find a rational ring triangle of area 5.