I remember once having access to that member number, but have long since forgotten how to access it. I used to copy early posts to a 3.5 inch drive and still have a computer with one but that computer has been parked for years.
IIRC you used to be able to see your member number in the URL of a particular page. I just went through every page connected to my account that I could think of and couldn’t find it. If there is still a way to do it I didn’t figure it out.