how many maximum series number have 2apx05 prod. code.
CREATE TABLE "table1_21994729_3" (
  "series_num" real,
  "season_num" real,
  "title" text,
  "directed_by" text,
  "written_by" text,
  "original_air_date" text,
  "prod_code" text
);
SELECT MAX("series_num") FROM "table1_21994729_3" WHERE "prod_code"='2APX05';