The denominator of 17 / 1001 is 1001.
The denominator of (x + x^2) / (x + 2 * x^2 + 1) is x + 2 * x^2 + 1.
The following object is not a fraction.
The denominator of (x + 1) / (x + 2) * (x + 3) / (x + 4) is 1.
The following object is not a fraction.
The denominator of exp(x / 4) is 1.
