CREATE TABLE table_3537 ("Series #" FLOAT, "Season #" FLOAT, "Episode Title" TEXT, "Original airdate" TEXT, "Prod. No." TEXT)

How many episodes had production number 2x13?
SELECT COUNT("Season #") FROM table_3537 WHERE "Prod. No." = '2x13'
SELECT COUNT("Season #") FROM "table_3537" WHERE "Prod. No." = '2x13'