Renumbering non-sequential files

[norman1312]

I have lots of files (thankfully in different folders) that contain a four digit number in the filename. This number is not necessarily sequential.
I can see how to delete the number and create a sequential set of filenames, but how can I maintain the original sequence?
Yes there is a valid reason why I want this but it's far too complex to explain here.

[Admin]

Hi, what original sequence? thanks

[norman1312]

Say the original numbers are 1, 2, 4, 5 then I don't want to renumber them 101, 102, 103, 104, but 101, 102, 104, 105 this keeping the ORIGINAL numbering scheme intact.