1. Select a range in an open column (say rows 1-500).
2. Enter: =IF(MOD(ROW(),2)=0,1,"e") and press
<ctrl><enter>.
3. Press F5.
4. Special > Formulas and uncheck each box
except "Number" (or "Text", depending on which rows you
wish to delete).
5. Press <ctrl><->
6. Select "Delete entire row".