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_21716139_1 ( category VARCHAR, train_no VARCHAR )

### Question ###
What is the category for trains numbered 16609/16610?

### Accurate SQL ###

SELECT category FROM table_21716139_1 WHERE train_no = "16609/16610"