"Ken Wright" wrote...
You are correct in that WEEKNUM is a PITA function that does not work
in an array. :-(
....

So improvise. If x were an array and you wanted what should be the array
result from WEEKNUM(x), try

=1+INT((x-DATE(YEAR(x),1,1)+WEEKDAY(DATE(YEAR(x),1,1),2))/7)