Copying a formula with different sheet refs
 

I need to fill in the formula, "=IF(MAX(Sheet2!B5:B200)(TODAY()-21),"not
due","due")" in sheet1 from cell b2 to B200 but to change only the Sheet ref
so that b3 refers to sheet3, and b4 refers to sheet4 and so on. When I try to
fill down, Excel changes the range of cells, not the sheet nos and if I try
to copy and paste, the same thing happens.
Would be grateful of any help please.