This function returns the day number of the month (integer 1 to 31) that corresponds to the specified date.
DAY(date)
Specify the date argument as a number (as in 37806.5) a string (as in "7/4/2003 12:00"), or a DateTime object, as in DATE(2003,7,4).
Accepts numeric, string, or DateTime object data. Returns numeric data.
DAY(A2)
DAY(R2C1)
DAY(366778) gives the result 14
DAY(33239) gives the result 1 (because 33239 is the value for January 1, 1991)
DAY("7/4/2003 12:00")
DAY(DATE(2003,7,4))