AMA Numbers
As I recall, originally, 1 & 2 digit numbers were for life members and 3 & 4 digit numbers were for contest directors. Regular members had 5 digits. This is probably all changed now since we have so many more members.
My original AMA was 32806. I lapsed for a while after I graduated from college and re-joined with 45531. When I became a CD in 1967, they gave me the 3 middle digits of my number, 553. I know, 3 digits and a repeat.
For several years now you can buy a vanity number just like a car tag. I knew one person who had his last name as his "number."