You can do this with a combination of formula and SEQ fields:

{ = 5*{ SEQ mynum } \# "00" }

To insert each pair of field delimiters, { }, press Ctrl+F9. Use F9 to update the field result. Alt+F9 shows/hides field codes.

You can make insertion easier by creating an AutoText entry with the field construct and the leading and trailing text.

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Stefan Blom
Microsoft Word MVP

Microsoft 365 apps for business
Windows 11 Professional