Put a space in a dynamic Number

Hello,
Does anyone know how to put a space beetween numbers, as following :
3 digits for thousands - space - 3 digits for hundreds

Here is expression I use :
ceil((time/comp.RenderEnd)*18350) .. " blah blah blah "

If I put a space between 18 & 350, then my counter doesn't work.

Please tell me if you have a trick.

Thanks

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Help with Number counter with commas (Text with separators)