Use a cell to refer to a tab

Hello, 

I am adding cell H26 of tabs named 1,2 & 3 using the following formula:

=SUM('1:3'!H26)

Instead of the number 3 in the above formula, I would like to be able to reference a cell to give me the tab name. That way if I add tabs I can easily update all the formulas.

Thanks 🙂