Hi Paul,
One way,
Put 1 into B1
Highlight B1 and B2
Grab the fill handle and drag down to row 4000
That should leave 1 blank 2 blank 3 blank...etc in col B
Put =INDIRECT("A"&B1) in C1
Grab the fill handle and drag down to C4000 (or just double click it)
That should leave your column A data in column C
separated by the #REF error.
Whilst column C is still selected
Tap F5>Special>Formulas
Uncheck Numbers, Text and Logicals and leave
Errors checked.
OK out
Then tap delete
Do a Copy>Paste Values on column C
and delete columns A and B
HTH
Martin