Macro to Open Correct Worksheet

[Mrs. Robinson]

I run a weekly macro that formats one of 52 worksheets based on information from another worksheet...appropriately named Wk 1, Wk 2, etc. Right now I use VLookup to get the data but would like to incorporate that into the macro. Is there a way to replace "Wk 33" (see below) so that I don't have to adjust the macro each week? If it helps, the Sheet #'s are also in numerical order, i.e. Sheet 1 is Wk 1, Sheet 2 is Wk 2, etc.

=VLOOKUP(B109,'[Approved vacation.xls]Wk 33'!$B$18:$F$94,5,FALSE)

Thanks,
Diana