Below is an instruction that describes a task. Write a response that appropriately completes the request.

### Instruction:
When did the series number 23 air?

### Inputs:
table_name: table, columns: ['Series no.', 'Title', 'Directed by', 'Written by', 'Original air date', 'Production Code']

### Response:
SELECT Original air date FROM table WHERE Series no. = 23