As the Pythagorean triple (s^2-t^2,2 s t,s^2+t^2), the equation x^2+y^2=z^r has the parametrizations for r\ge 2. By using them, we could give the convergents of certain values by rationals x/y such that x, y satisfy Diophantine equations. We can also give the Frobenius numbers formed from Diophantine equations. In this talk we consider the equations x^2+y^2=z^r for r=2,3,4,5.