What symbol represents the set of natural numbers?

ℕ

Who portrayed Margaret Thatcher in the movie "The Iron Lady"? Which 2013 film features Sandra Bullock and George Clooney stranded in space? Who is Aang’s earthbending teacher in "Avatar: The Last Airbender"? Who was the Egyptian goddess of fertility and motherhood? In 1795, the United States signed the Jay Treaty to resolve tensions with which nation?