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_name_81 (series__number INTEGER, directed_by VARCHAR, written_by VARCHAR)
### Question:
What series number was directed by milan cheylov and written by will dixon?
### Answer:
SELECT AVG(series__number) FROM table_name_81 WHERE directed_by = "milan cheylov" AND written_by = "will dixon"