Can anyone advise me how to autofill formulas which will take into account
the data is from different sheets please?

I have several sheets I am wanting to pull data from as a summary sheet, but
at the moment I am having to manually type in the formula for each sheet in
the summary. I have tried the drag auto fill but it only copies the existing
selection.

e.g. In cell A1, b1 and c1 respectivley I have entered =sheet1!b$4
=sheet1!c$21 =sheet1!c$20 and then correspondingly in the subsequent rows
below. The data is taken from the same cells in each workbook.