CREATE TABLE table_2818164_2 (production_code VARCHAR, original_air_date VARCHAR)

How many different production codes does the episode originally aired on October 18, 1984 have?
SELECT COUNT(production_code) FROM table_2818164_2 WHERE original_air_date = "October 18, 1984"
SELECT COUNT("production_code") FROM "table_2818164_2" WHERE "October 18, 1984" = "original_air_date"