How many u.s. viewers  (million) have 6 as the #?
CREATE TABLE "table1_2866456_1" (
  "no" real,
  "num" real,
  "title" text,
  "directed_by" text,
  "written_by" text,
  "u_s_air_date" text,
  "production_code" text,
  "u_s_viewers_million" text
);
SELECT "u_s_viewers_million" FROM "table1_2866456_1" WHERE "num"=6;