CREATE TABLE table_203_784 (id DECIMAL, "no. in\ series" DECIMAL, "no. in\ season" DECIMAL, "performer" TEXT, "appearance" TEXT, "air date" TEXT)

how many performers appeared on the air date 21 january 2011 ?
SELECT COUNT("performer") FROM table_203_784 WHERE "air date" = '21 january 2011'
SELECT COUNT("performer") FROM "table_203_784" WHERE "air date" = '21 january 2011'