user: Question: Which Subregion has a No P. of 4, and a Pop/Area (1/km²) of 534?
Columns: ['Name', 'Area (km²)', 'Pop.', 'Pop/Area (1/km²)', 'No P.', 'No C./No T.', 'Subregion']
Types: ['text', 'real', 'real', 'real', 'real', 'text', 'text']
Sample row: ['Águeda', 335.3, 47729.0, 148.0, 20.0, '1/?', 'Baixo Vouga']
SQL:

assistant: SELECT "Subregion" FROM "Table" WHERE "No P." = 4.0 AND "Pop/Area (1/km²)" = 534.0;