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_15 (city_population__2009_ INTEGER, serial_no VARCHAR, city_area_km_2__ VARCHAR, district VARCHAR)

### Question ###
What was the lowest city population for the district of rajanpur district with a area of 6 km squared and a serial number less than 29?

### Accurate SQL ###

SELECT MIN(city_population__2009_) FROM table_name_15 WHERE city_area_km_2__ = 6 AND district = "rajanpur district" AND serial_no < 29