SharePoint online - search for documents containing #147 only

My manager would like to search SharePoint for only files that contain the phrase #147

(This is how some projects have been referred to in files in the past)

I would have thought that using double quotes like "#147" would do that.

But it seems not.

If I search SharePoint for "#147" it will return every file with 147 in it. 

For example "Timetable for bus number 147" or a file with a figure such as £147 or $147 in it.

How can I make SharePoint only return files with #147 in them?

thanks in advance.