The phone interview was a very pleasant experience, although we didn't move forward. They emailed me a few days later to let me know that they currently don't have a position for me.

All the tasks I had to solve weren't hard at all. However, because you probably haven't thought about them before in the way they asked, you might feel confused, but only at first.

The whole interview lasted for an hour, and at the end, the interviewer (who is, of course, employed at Jane Street) talked about some projects they do and how they do them.

Using some functions that were provided, which operate with cells in spreadsheets, I had to compute the sum of an array.

Later, I had to implement those functions myself. The trickiest thing was implementing the part where some cell is a sum of two other cells, and some of those two cells are themselves sums of other cells, and so on.