CREATE TABLE table_37242 ("Week" FLOAT, "Date" TEXT, "Opponent" TEXT, "Result" TEXT, "Venue" TEXT, "Attendance" FLOAT)

Opponent of at san francisco 49ers had what lowest week?
SELECT MIN("Week") FROM table_37242 WHERE "Opponent" = 'at san francisco 49ers'
SELECT MIN("Week") FROM "table_37242" WHERE "Opponent" = 'at san francisco 49ers'