Do sum up cell A1 of each worksheet from 1 to 6 I would use this function:
=SUM(Sheet1:Sheet6!A1)

BUT what if I don't know how many worksheets I will be having. Maybe 50 or
100.
How can I write a function to sum up all the worksheets?

When I use this formula:
=SUM('*'!A1) It works if you know how many you will have, but not if you
keep adding more. Because that function above turns into this
=SUM(Sheet1:Sheet6!A1) - depending how many worsheets you have, so if you
would add a 7th, it would not count that.

Anyone have any suggestions?

Thank you