How many crew members worked as producer in the movie "Pirates of the Caribbean: At World's End"?
worked as producer refers to job = 'Producer'; "Pirates of the Caribbean: At World's End" refers to title = 'Pirates of the Caribbean: At World''s End'
SELECT COUNT(T3.person_id) FROM movie AS T1 INNER JOIN movie_crew AS T2 ON T1.movie_id = T2.movie_id INNER JOIN person AS T3 ON T2.person_id = T3.person_id WHERE T1.title LIKE 'Pirates of the Caribbean: At World%s End' AND T2.job = 'Producer'