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_name_21 (airing_date VARCHAR, genre VARCHAR, number_of_episodes VARCHAR)

### Question ###
What is the airing date for a modern drama with more than 21 episodes?

### Accurate SQL ###

SELECT airing_date FROM table_name_21 WHERE genre = "modern drama" AND number_of_episodes > 21