for (int i = 1; i = 20; i++)
{
int j = i * i;
if (j >= 50)
Response.Write(i + " × " + i + " = " + j + "br />");
}

int min = (int)Math.Sqrt(50);

if (Math.Pow(min, 2) 50)
min += 1;

for (int i = min; i = 20; i++)
{
int j = i * i;
Response.Write(i + " × " + i + " = " + j + "br />");
}