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_7 ( gdp__ppp__$m_usd VARCHAR, population_density__per_km²_ VARCHAR )

### Question ###
How much is the GDP for a population density of 254.7?

### Accurate SQL ###

SELECT gdp__ppp__$m_usd FROM table_name_7 WHERE population_density__per_km²_ = "254.7"