CREATE TABLE table_647 ("Week" FLOAT, "Date" TEXT, "Opponent" TEXT, "Result" TEXT, "Game site" TEXT, "Record" TEXT, "Attendance" FLOAT)

Name the number of opponent with arrowhead stadium
SELECT COUNT("Opponent") FROM table_647 WHERE "Game site" = 'Arrowhead Stadium'
SELECT COUNT("Opponent") FROM "table_647" WHERE "Game site" = 'Arrowhead Stadium'