Initial phone screen followed by take home test (well documented on the blog, it's worth reading over this before you do anything). Typical enough, flatten array, compute primes, compute multiples. Very manageable stuff. Be sure to include test cases for everything.
If you pass this you will be invited to a technical live coding session. This is pretty typical, I would recommend knowing basic algorithms and programming concepts, i.e. sorting, recursion etc.
Following this is a non-technical phone call to assess culture fit. Just be generally enthusiastic and chatty, they want to see that you aren't just in the interview for the laugh!
Passing this will bring you to an onsite interview, which is broken into 4/5 separate interviews. Some are non-technical, and others are more so, i.e. whiteboarding, pair programming etc.
Overall it's a pretty manageable interview process, but you need to know the product and your basic CS concepts.