Special RegEx Patters

I am trying to search for a specific pattern using regex, but I am having a difficult time. I have over 4,000 images, named as three different file sets, named like so...

• 0001234_name-of-file.jpeg
• 0001235_name-of-file_100.jpeg
• 0001236_name-of-file_200.jpeg

What I want to do is JUST search for the files like 0001234_name-of-file.jpeg

I do NOT want any of the files that have the _100 or _200 at the end before the extension.

Any help would be greatly appreciated.

Cheers,

~D