How many successors were seated in the New York 20th district?
CREATE TABLE "table1_1199219_2" (
  "district" text,
  "vacator" text,
  "reason_for_change" text,
  "successor" text,
  "date_successor_seated" text
);
SELECT COUNT("successor") FROM "table1_1199219_2" WHERE "district"='New York 20th';