Multi-staged. First stage was a relatively manageable mental math test. Second stage was one of the most challenging coding challenges I've received for internship applications, with very algorithm-oriented problems. There are supposed to be two-three stages following this, all of which are technical intwrviews. I was only able to make it to the interview that immediately followed, which was a technical interview focusing on recent math you have done. What would've followed was a coding-based technical phone interview.