Which series episode has a netflix figure of s04e21?
CREATE TABLE "season_8_2006_2007" (
  "series_ep" text,
  "episode" real,
  "netflix" text,
  "segment_a" text,
  "segment_b" text,
  "segment_c" text,
  "segment_d" text
);
SELECT "series_ep" FROM "season_8_2006_2007" WHERE "netflix"='s04e21';