CREATE TABLE table_24880 ("No. in series" FLOAT, "No. in season" FLOAT, "Title" TEXT, "Directed by" TEXT, "Written by" TEXT, "Original air date" TEXT, "Production code" TEXT)

Who is the writer of episode 13?
SELECT COUNT("Written by") FROM table_24880 WHERE "No. in season" = '13'
SELECT COUNT("Written by") FROM "table_24880" WHERE "No. in season" = '13'