Below is the list of tables from the database along with their columns and datatype. Need to generate an accurate SQL query for the question.
Only use the columns present in the respective table. Only use the columns which are required to generate the SQL query. Only use table joins if required and not otherwise.

### Tables ###
TABLE: CREATE TABLE table_30366 ( "No. in series" real, "Title" text, "Directed by" text, "Written by" text, "Original air date" text, "Production code" real )

### Question ###
How many different production codes does the episode originally aired on October 18, 1984 have?

### Accurate SQL ###

SELECT COUNT("Production code") FROM table_30366 WHERE "Original air date" = 'October 18, 1984'