Conversation so far:
what is the main idea of captain underpants
The Captain Underpants children's novel series revolves around Captain Underpants, a superhero from two fourth-graders' homemade comic books, who becomes real.
when was the captain underpants first published
The first novel in the Captain Underpants series, The Adventures of Captain Underpants was published on September 1, 1997.
Who is the author of the Captain Underpants series?
Captain Underpants is an illustrated children's novel series by American author and illustrator Dav Pilkey.

Question: how many books have been released
Self-contained rewrite: How many Captain Underpants books have been released?