CREATE TABLE table_3961 ("Series #" FLOAT, "Season #" FLOAT, "Title" CLOB, "Directed by" CLOB, "Written by" CLOB, "Original air date" CLOB, "Production code" CLOB, "U.S. viewers  ( million ) " CLOB)

What episode number in the series had a production code of bdf405?
SELECT MIN("Series #") FROM table_3961 WHERE "Production code" = 'BDF405'
SELECT MIN("Series #") FROM "table_3961" WHERE "Production code" = 'BDF405'