Yes, however much of the difficulty of AoPS is the depth and not necessarily different topics (although they do cover topics outside the normal scope).
For example, within sequences and series, they cover arithmetic sequences and series, geometric sequences and series, telescoping sequences and series, recursive series, Sigma notation, and nested sums, plus a few other topics.
ETA: Sequences, series, and induction definitely are difficult. Those three chapters are considered among the most difficult in Intermediate Algebra.