How many people wrote the episode that had 6.34 million viewers?
CREATE TABLE "table1_17641206_2" (
  "episode" real,
  "title" text,
  "directed_by" text,
  "written_by" text,
  "original_airdate" text,
  "duration" text,
  "viewership" text
);
SELECT COUNT("written_by") FROM "table1_17641206_2" WHERE "viewership"='6.34 million';