Are arithmetic sequences and series even tested on the ACT? I'm using Barron's 36 and I have never even seen this stuff before. Should I bother to remember it?

Arithmetic sequences are pretty rare on the ACT - you'll see a question (never more than one) asking about them once every 2-3 tests. As we advise in our blog article on sequences in the ACT Math section, you should only study sequences once you feel you have a good grasp of the other more common ACT Math topics like angles, integers, ratios, slopes, and triangles.

Basically, **if you're already good on all of those topics and are aiming for a perfect score on the math section, make sure you know how to answer sequence questions.** Otherwise, focus your attention on areas that'll net you more points.