Select A1 and A2 (where you have 1 and 2 already entered) and copy down using the fill handle (AutoFill).
Aladin
If you like hot keys...Put 1 in a1, 2 in a2, up arrow twice, hold the shift key and press page
down, then hold down ALT E,I,S, Step value = 1...then hit enter.
Should end up with 1 to 28.
After selecting cells A1:A10 choose the Edit Fill
Series... menu command and press OK.
Just in case the first three ways weren't enough, here is another.
Put 1 in A1
Put the arrow on the fill thingy (technical term) in the lower right corner.
Hit the right mouse button and put down as far as you need to.
Release the right mouse key and select Fill Series
After a1=1 and a2=2, go back to a1, then hold the shift key...while holding the shif key
press PageDown. This will select a1:a27. Then hit the ALT key 1 time...then hit 'E'(Edit), then 'I'
(Fill),then 'S'(Series)...Make sure the step value is set to '1' and hit enter...
It will paste 1 - 27 in A1:A27.