We mostly looked at problems with sigma notation. At the bottom of the capital (Greek) letter Sigma, there is a variable with the starting point and at the top a finishing point if it is finite or infinity.
Then the sequence of numbers goes into an equation that are added together.
For a geometric series, there can be a finite sum or it can diverge.
Exponents can be used, and series can also alternate between positive and negative. You can describe the same series in ways that look different.
Looked a bit at combinations and permutations, including one that required a somewhat seldom used formula at least in high school math classes.