Totaling Moving Values by Week

Hi Everyone,

I have an attached spreadsheet.

If you take a look a tab 2, sheet 1, I have a data setby cohort and their assumed retention curve.

Row 2 has the total number rof people in that group.

In the summary page, I'd like to roll up the number of users by Week.

So Week 1 would be 2458 users.

Week 2 would be (2458 * 29%) + 3979 and so on as a cohort matures. How can this be designed?