reference a cell from another worksheet using a variable

I'm trying to refer to another worksheet (BASE tab) in the same workbook. I run the code below inside a couple of loops where x and y increment based on certain conditions. I've messed around with the code but I haven't had any luck. This is what I have so far but it does not work.

Cells(i, j) = "='BASE tab'!R[" & x & "]C[ & y & ]"

I want cells(i,j) to reference the other cells so I don't have to run my lengthy macro for minor value changes.