user: Question: The successor for the Massachusetts 20th district was seated on what date?
Columns: ['District', 'Vacator', 'Reason for change', 'Successor', 'Date successor seated']
Types: ['text', 'text', 'text', 'text', 'text']
Sample row: ['Connecticut At-large', 'Uriel Holmes (F)', 'Resigned sometime in 1818', 'Sylvester Gilbert (DR)', 'Seated November 16, 1818']
SQL:

assistant: SELECT "Date successor seated" FROM "Table" WHERE "District" = 'Massachusetts 20th';