What is the original air date of the episode that was number 31 in the series? 
CREATE TABLE "table1_29584044_1" (
  "no_in_series" real,
  "no_in_season" real,
  "title" text,
  "directed_by" text,
  "written_by" text,
  "original_air_date" text,
  "production_code" real
);
SELECT "original_air_date" FROM "table1_29584044_1" WHERE "no_in_series"=31;