What is the production code for the number 5 series ? 
CREATE TABLE "table1_26801821_1" (
  "no_in_series" real,
  "title" text,
  "directed_by" text,
  "written_by" text,
  "original_air_date" text,
  "production_code" text,
  "u_s_viewers_millions" text
);
SELECT "production_code" FROM "table1_26801821_1" WHERE "no_in_series"=5;