MathCastle
Proof WritingChallengeDirect Proof

Direct Proof · Challenge problem

The identity (a2+b2)(c2+d2)=(ac−bd)2+(ad+bc)2(a^2 + b^2)(c^2 + d^2) = (ac - bd)^2 + (ad + bc)^2 shows that a product of sums of two squares is again one. In how many ways can 1105=5⋅13⋅171105 = 5\cdot13\cdot17 be written as x2+y2x^2 + y^2 with integers 0<x<y0 < x < y?