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_11951237_1 ( written_by VARCHAR, series__number VARCHAR )

### Question ###
Who were the writers for series number 20?

### Accurate SQL ###

SELECT written_by FROM table_11951237_1 WHERE series__number = 20