Syntax:
DAYNAME(value:(Number|Date)
Returns a text string of the day given by value.
value must be either a number or date value.
If value is a number, usually number 1 represents Sunday, 2 being Monday through 7 being Saturday. Numbers outside the range [1,7] are reduced into this range,
Examples:
DAYNAME(7)
returns the text string "Saturday"
DAYNAME(WEEKDAY(TODAY))
returns today's day name as a text string.