Question: The Heroes of Olympus is a pentalogy of adventure, mythological fiction and fantasy novels by American author Rick Riordan that collectively form a sequel series to the Percy Jackson & the Olympians series, a pentalogy of adventure and mythological fiction books written by which American author ?
Sentence (from "Percy Jackson &amp; the Olympians"): More than 45 million copies of the books have been sold in more than 35 countries.
Relevant evidence: No