I have adopted Optimus assuming it would support integers up to 2^32-1.

Is there a technical reason why it is limited to 2^31-1? Is it that the method only works when the max integer is prime number?

I would be happy to submit a PR to make the range configurable. But I don't fully understand the maths to know if there's a logical problem with this.

In terms of the maths, why is a large prime preferred over a small prime?