public static bool IsTriangle(long n)
{
double upper = ((-1 + Math.Sqrt(1 + 8 * n)) / 2);
return(FloatingPointEquals.IsEqualToLongWithPrecision(upper, (long)upper, 5));
}
public static bool IsSquare(long n)
{
double upper = (Math.Sqrt(n));
return(FloatingPointEquals.IsEqualToLongWithPrecision(upper, (long)upper, 5));
}
public static bool IsHexagonal(long n)
{
double upper = ((1 + Math.Sqrt(1 + 8 * n)) / 4);
return(FloatingPointEquals.IsEqualToLongWithPrecision(upper, (long)upper, 5));
}