<p>White Rabbit, I think the math sequences are designed so that jump from 21 and 23 is doable, even for a person who has only taken ap calculus in high school. If you don’t think you can handle 23, then I think the math department recommends you taking a course in 100 series to learn how to proof things before diving into algebra, analysis, and topology. However, this all depends how far you want to go in math. If you plan to major in it, the better idea is probably to take 23 or 25 (though finals for the latter look like coded Egyptian hieroglyphics).</p>