Applied online and had a phone call with the recruiter.

I asked for some time before having the phone interview to prepare myself, as I haven't done those in a while, and they had no issues with that.

Once I felt ready, I got scheduled for a 45-minute phone interview.

The interview questions themselves were not that hard, but I did make some silly mistakes in the implementation of corner cases, which I caught myself later when the interviewer asked me to test a few values on the function.

The interview was very fast-paced. The interviewer jumped straight to the questions, with no chatting about my resume or anything else before the tech questions.

The interviewer was also very aggressive, so my advice for you is to show confidence and relax.

I haven't done these interviews in a while, so in the end, while my answers were correct, I felt the pressure and failed.

That aggressiveness seems to be part of their interview process, so again, just show some confidence, trust your answers, and as long as you have the right answers and test your code correctly, you should be fine.

The recruiter was great during the entire process (kudos).

Implement a function to return the power of a number. Once I got that right, I was shown a class implementation and asked if that was immutable.