The opening paragraphs of American Airlines 2017 10-K states:
there were 473,138,683 shares of American Airlines Group Inc. common stock outstanding
there were 1,000 shares of American Airlines, Inc. common stock outstanding, all of which were held by American Airlines Group Inc.
Why 1,000 shares? I read that American Airlines, Inc. is a wholly-owned subsidiary of American Airlines Group Inc. Is this a convention for subsidiaries?
United Airlines' 10-K shows an identical situation, where 1,000 shares of United Airlines, Inc. common stock are 100% owned by United Continental Holdings, Inc.