Who is the directed by when 2t6404 is the production code?
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 "directed_by" FROM "table1_2866456_1" WHERE "production_code"='2T6404';