CREATE TABLE table_26406 ("Series #" FLOAT, "Season #" FLOAT, "Title" TEXT, "Directed by" TEXT, "Written by" TEXT, "Original air date" TEXT, "Prod. code" FLOAT)

What is the production code for episode 31 in the series?
SELECT MIN("Prod. code") FROM table_26406 WHERE "Series #" = '31'
SELECT MIN("Prod. code") FROM "table_26406" WHERE "Series #" = '31'