Pythagorean triple with not optimal bound

PythTriple.cs

var soln = new List<(int a, int b, int c)>();

// Bound for a
// NOTE: this is a first guess, we'll do better later
// a + b + c = N => If all are equal, upper bound is N/3
double aMax = n / 3.0;

for (int a=1; a<aMax; a++)
{

  // b = (N^2 - 2Na) / (2N - 2a)
  int num = sum * sum - 2 * sum * a;
  int denom = 2 * sum - 2 * a;
  if (num % denom != 0)
  {
      continue;
  }
  int b = num / denom;

  // c = N - a - b
  int c = sum - a - b;  
  
  soln.Add((a, b, c));
}