Regex expression error in Formula tool

Hi,

Having a problem here - would be so much appreciated if anyone can provide the solution.

to identify any digit character(s) in a field and to replace with a string letter(such as F) to a string letter and any digit character(s):

to    

I used Formula tool with an expression: REGEX_Replace([Column], "\d{0,}", "F\d{0,}")

tested the regex terms in Regexer.com, and it works well there. However, when applying the same expression on Alteryx, it gives me weird answers:

Or an any other function/tool would achieve the same result rather than using RegEx?

Any help would be appreciated!

Thanks in advance!

Zoey