CREATE TABLE table_16984 ("Series #" FLOAT, "Season #" FLOAT, "Title" TEXT, "Directed by" TEXT, "Written by" TEXT, "Original air date" TEXT, "Production code" FLOAT)

What is the number of series with production code 503?
SELECT COUNT("Series #") FROM table_16984 WHERE "Production code" = '503'
SELECT COUNT("Series #") FROM "table_16984" WHERE "Production code" = '503'