What is the episode # of the episode that originally aired on January 21, 2001?
CREATE TABLE "season_5_2001" (
  "episode_num" text,
  "title" text,
  "directed_by" text,
  "written_by" text,
  "original_airdate" text
);
SELECT "episode_num" FROM "season_5_2001" WHERE "original_airdate"='january 21, 2001';