How to display name day of the week in every cell in one column in iOS Numbers (sun, mon, etc)

I'm not sure I understand your question.

> but short of doing fill down over and over in column A, how do I get every subsequent cell in

column A to have that formula

That's precisely what Fill Down is there for - to fill a column of cells with a consistent formula.

It's also only two clicks (either select column A header and use Table -> Autofill -> Autofill Down, or select cell A1 and drag the handle at the bottom of the cell down to the bottom of the table.

What am I missing here? Maybe I'm not understanding why you think you need to do this 'over and over'...?

Oh, my bad. I didn't notice this was for iOS. The menu options are MacOS-specific, since iOS apps don't have the same menu structure.

The rules are a little different on iOS, with the Select -> AutoFill -> Drag method as being the standard.

TBH, though, I don't use Numbers for iOS as much, so I'll keep poking.

You could amend the formula to check for blank B values, for example:

=IF(ISDATE(B2),DAYNAME(B2),"")

which first checks to see if the referenced cell is a date. If so, it returns the DAYNAME(), otherwise it returns an empty string.