To Know: The first assessment is 95% graded and you’ll get detailed solutions back, and then I’m happy to chat about the (unintionally) hard counting problem that was in there! Another day or two.

Play with the Big-O notation interactive (I think it’s fixed again now). In particular, read the text at the top of the page — it suggests a few small exercises. You need to click away from a box after changing something to get the graphs to update.

Please Read Section 3.6 (skipping 3.6.1 if you like) and 3.7 of your textbook. Please read actively.Everything here is considered part of the material we have covered. The book takes a somewhat different approach to the modular arithmetic, so this is at once the same material we have been covering, and a different take on it. One thing that is new and we will come back to, is the formula for Euler’s phi-function. The book does it depending on the chinese remainder theorem, which we haven’t covered yet, so you can skip the justification, but it is nice to look at and be able to use the formula. The rest should look like a bit of a remix of things we’ve seen. Take the time to line it up, conceptually, with the things we’ve seen (particularly the “sum-up” from the last lecture).

To hand in:

(1) Use the formula for Euler phi from the book to compute phi(15) and phi(45), showing your work.

(2) Tell me three things you learned from the reading.