I have a worksheet that has multiple pages. In one cell there is a formula
that references a cell within that worksheet and then adds it to a cell from
the previous worksheet. Every week this worksheet is copied for the new week
using the "move/copy function". I would like for this cell to automatically
change to the previous worksheet without having to manually change it.

Ex. =sum(i17+'week1'!i20) This is the content of the cell in week 2.
=sum(i17+'week2'!i20) This is the content of the cell in week 3.
=sum(i17+'week3'!i20) This is the coentent of the cell in week 4.
I would like for the reference to the previous week to automatically advance
to the next week. Any suggestions???