fill series

Hi all,

I think this is an easy one for some experts out there but my knowledge of excel is limited.

I need to fill a series in a column. The cells that need filling make reference to another cell. example cell c1 has =a5, cell c2 has =a8, cell c3 has =a11. they increment by +3 each time... i need to fill down the "c" column about 1000 cells.
How do i do this with the auto fill feature or any feature as long as its not manual??

thanks,

Thanks buddy,
I replaced the -1 with -3 and works great..

much appreciated. saved me many hours