Below is an context that describes a sql query, paired with an question that provides further information. Write an answer that appropriately completes the request.  # noqa: E501
### Context:
CREATE TABLE table_19236587_4 (original_air_date VARCHAR, series_no VARCHAR)
### Question:
How many different original air dates does the episode with series number 13 have?
### Answer:
SELECT COUNT(original_air_date) FROM table_19236587_4 WHERE series_no = 13