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_23937219_3 ( prod_code INTEGER, series__number VARCHAR )

### Question ###
What is the production code for episode 31 in the series?

### Accurate SQL ###

SELECT MIN(prod_code) FROM table_23937219_3 WHERE series__number = 31