When 6.66 is the amount of viewers what is the lowest production code?
CREATE TABLE "table1_24781886_2" (
  "num" real,
  "title" text,
  "director" text,
  "writer_s" text,
  "viewers" text,
  "air_date" text,
  "production_code" real
);
SELECT MIN("production_code") FROM "table1_24781886_2" WHERE "viewers"='6.66';