MathCastle
Number TheoryHardDiophantine Equations

Diophantine Equations · Hard problem

Every positive integer n≡1(mod4)n \equiv 1 \pmod 4 passes the mod-44 test for being a sum of two squares. How many n≡1(mod4)n \equiv 1 \pmod 4 with 1≤n≤601 \le n \le 60 are nevertheless not of the form x2+y2x^2 + y^2 with integers x,yx, y?