Continuing a list with text and numbers

I want to fill a column with image ID numbers followed by a suffix ie, "001.jpg" without the speech marks, and have Excel continue the list down the column, but I can't get the ".jpg" part to copy, only the numbers, so at present I am filling in each cell which takes forever!
Is there an easy to do this?
The actual total of numbers will vary each time - it is for a photography web-site, but each one needs the identifier after the number without a space.
Can someone suggest a step-by-step method of doing this if it is possible and is there a way to save the "formula" for further use?
I hope someone can help as this is driving me mad!