Use the fill handle to drag a single number down a column
Enter 1 in the first cell and 2 in the next cell, then drag both cells down
Use the formula `=ROW()` to generate serial numbers
Use the formula `=ROW(A1)` and copy it down
Use the formula `=SEQUENCE(n)` in Excel 365 or Excel 2021
Use `=ROWS($A$1:A1)` and fill down
Use `=COUNTA($A$1:A1)` if you want serial numbers based on nonblank entries
Use `=IF(A1<>“”,ROW()-ROW($A$1)+1,””)` to number only filled rows
Use `=SUBTOTAL(3,$A$1:A1)` for serial numbers that ignore filtered-out rows
Use AutoFill from the Home tab using Fill > Series