My interview process started with a written math test (simple arithmetic) that I completed in a classroom with 20 others from my university. You get the results back immediately, and 3 out of 20+ of us were told that we passed. After a quick 1v1 interview with their hiring manager, there's an all-day interview process at their office, which begins with 2 more math tests and ends with 3 1v1 interviews. The 1v1 interviews were of very high caliber; the last one intellectually crushed me so bad I was very uncertain whether I would get the job. There were no simple brainteasers, I think the 3 math tests are used to filter out anyone without above average intelligence, and their 1v1s are meant to really drill down and see how you solve difficult problems under stressful conditions.